Simple Sensible Solutions

TM 

Simple, Sensible, Solutions ® 

A GROWER’S GUIDE TO FINISHING PERENNIALS. 7TH EDITION. 

www.WaltersGardens.com • 1-888-925-8377 • sales@waltersgardens.com | 1

Table of Contents 

Product Profile 3 - 5 

Bare Root 6 - 9 

Plug / Liners 10 - 13 

Culture Guide 14 - 28 

Grower’s Reference Chart 29 - 33 

Plant Health 34 - 37 

Summer / Early Fall Planting & Overwintering Recommendations 38 - 42 

Additional Resources 43 

Walters Gardens 

Home of Proven Winners® Perennials 

P.O. Box 137 • Zeeland, MI 49464 • Phone: 888-925-8377 • Fax: 800-752-1879 • Email: sales@waltersgardens.com 

www.WaltersGardens.com • www.PerennialResource.com • www.ProvenWinners.com 

Disclaimer of Liabilities: While every effort has been made to ensure the accuracy of the information provided in this growers guide, Walters Gardens, Inc. makes 

no guarantee, express or implied, as to the procedures contained here. Walters Gardens, Inc. will not be liable for direct, indirect, incidental or consequential 

damages in connection with or arising from the furnishing, performance, or use of this booklet. 

© Walters Gardens, Inc. 2019 

2 | Walters Gardens

Product Profile 

Timing Chart 

Product Size When to Plant Finish Size Average Finish Time 

General Perennials #1 Grade Late Summer - Early Spring 1-gal 6-10 wks 

#2 Grade Late Summer - Early Spring 1-gal 8-12 wks 

#3 Grade Late Summer - Early Spring 1-qt 4-6 wks 

20ct plugs Early Spring 1-gal 6-10 wks 

30ct plugs 

72ct plugs 

128ct plugs 

Early Spring 

Spring 

Late Summer 

Early Spring 

Spring 

Late Summer 

Early Spring 

Spring 

1-gal 

1-qt 

1-gal 

1-qt 

6-pk 

1-gal 

1-qt 

6-pk 

6-10 wks 

4-6 wks 

8-10 wks 

4-6 wks 

3-4 wks 

12-16wks 

5-8wks 

4-5wks 

Hibiscus #1 Grade Spring 3-gal 8-10 wks (flowers in 14-16 wks) 

72ct plugs Spring 2-gal 10-12 wks (flowers in 14-16 wks) 

Hosta 20ct plugs Midsummer - Early Spring 

Late Summer 

72ct plugs 

Late Spring - Early Summer 

Midsummer - Late Summer 

Early Spring 

1-gal 

1-qt (Mini Hosta) 

1-gal 

1-qt 

6-pk 

8-10 wks 

6-10 wks 

16-20 wks 

8-10 wks 

6-8 wks 

Succulents 72ct plugs Early Spring - Late Spring 1-qt 20-24 wks 

Mangave 72ct plugs Early Summer 1-qt 10-14 wks 

Tropicals 20ct plugs Early Spring 

Early Spring 

72ct plugs 

Spring 

Early Spring 

1-gal 

2-gal 

4-in 

1-gal 

* Finish times vary by variety and growing environment (temperature, water, amount of light, fertilizer, etc.). 

6-10 wks 

10-12 wks 

4-6 wks 

8-10 wks 

Based on zone 5, min 

55-60ºF constant ghse temp 

Based on zone 5, 65-70ºF or 

warmer natural temps 



We’re Your Biggest Fan 

We grade ahead of the curve 

to give your daylilies more 

fans and fuller containers. 

Our Crowning Achievement 

We’ve got our eyes on the 

prize. Our goal is larger crowns 

and more rewarding results. 

The Root Cause 

Our sandy fields promote fast 

root growth to ensure that 

what’s below matches what’s 

above. 

Bare Root 

As the largest wholesale grower of bare root perennials in North America, we offer the widest selection of generously graded varieties. Most 

are grown for one season and are sold as #1 grade transplants or divisions. Hemerocallis, Hosta, and select perennials that require it are grown 

for two seasons in order to offer the best product. Our most popular varieties are offered in economically priced #2 and #3 grade divisions. 

#1 Grade (G1) 

Most #1 grade perennials are one year 

plants or generously graded divisions of a 

one year plant. #1 Grade Hemerocallis and 

Hosta are sold as 3-5 eye/fan divisions of 

a two year field clump depending on the 

variety. Intersectional peonies are sold as 

divisions of a two year field clump. 

Count: sold in multiples of 25 

Minimum order: 1 box of 25 

4 | Walters Gardens 

#2 Grade (G2) #3 Grade (G3) 

Most #2 grade perennials are one year 

plants or divisions of a one year plant. #2 

Grade Hemerocallis and Hosta are sold as 

smaller 2-3 eye/fan divisions of a two year 

field clump. 


Minimum order: 1 box of 100 

Select Hemerocallis and Hosta varieties 

are sold as a #3 Grade division. These are 

some of our most popular varieties offered 

in an economical 1-3 eye/fan division of a 

two year field clump. 


Minimum order: 1 box of 250


Plug Liners 

Many of the products offered in this catalog are grown in plug form. Several sizes are available including 20, 30, 72, and 128 count. The 

majority of our plugs are easy to transplant Elle Plugs, while others are traditional loose fill plugs. The type of plug used is based upon the 

specific needs of the plant. 

Larger 20 and 30ct plugs are best suited to customers looking for faster turnaround times and sales the same season. Smaller 72 and 

128ct plugs are better suited for growers looking to produce larger quantities at a lower input cost. They are typically planted in summer 

for sales the following spring. 

We offer a number of perennials in economically priced 72 and 128ct plugs which are ideal for growers looking to produce larger quantities 

of their best selling items at a lower input cost. Don’t see exactly what you’re looking for? We accept custom orders for 72s and 128s 

(minimums apply). Please contact us for details. 

Size Plug Measurements Minimum Order 

20ct Elle Tray 31/4” deep x 23/4” wide 1 Tray of 20 

20ct Deep Cell Tray 41/2” deep x 23/4” wide 1 Tray of 20 

30ct Elle Tray 3” deep x 2” wide 1 Tray of 30 

30ct Deep Cell Tray 41/4” deep x 2” wide 1 Tray of 30 

72ct Elle Tray 21/2” deep x 11/3” wide 1 Tray of 72 

128ct Elle Tray 2” deep x 11/8” wide 1 Tray of 128 


Bare Root 

Walters Gardens is one of the largest field growers of perennials in the US, with over 1,500 acres dedicated to bare root production. In West 

Michigan, we are blessed with sandy loam soil and moderate temperatures from our close proximity to Lake Michigan. Perennials thrive in 

our fields, most reaching saleable size in just one growing season. 

Our bare root perennial guide is meant to help you with the entire process of growing our perennials to finished size. To learn more about 

our bare root sizes, see p. 4. 

Roots 

Fibrous Root 

Taproot 

Rhizome 

Corm 

A mass of profusely branched 

roots, often with no main taproot. 

Typically easy to divide. 

Ex: Achillea, Veronica, Daylilies 

The main descending root of a 

plant, often with little branching. 

Division is not recommended. 

Ex: Gypsophila or Baptisia 

A horizontal underground stem 

with branching close to the soil 

surface. Roots and shoots are 

often produced along its length. 

Ex: Siberian Iris 

A solid, underground, bulb-like 

portion of the stem of a plant 

bearing roots at the base. 

Ex: Crocosmia 

Divisions 

Eye 

A bud or shoot atop the crown of a 

plant from which foliage grows. Some 

perennials that are graded by their 

number of eyes include Paeonia, 

Astilbe, and Hosta. 

Fan 

A fan refers to an individual unit of a 

clump that includes one crown with 

a set of leaves and roots attached. 

Hemerocallis are typically graded by 

their number of fans. 

6 | Walters Gardens

Bare Root 

Scheduling delivery of your bare root perennials 

As a grower, you know that timing is everything. Sometimes it takes 

a little experimenting to figure out what works best in your specific 

climate. To help take the guesswork out of finishing your bare root 

perennials, we offer you some guidelines in our timing chart on p. 3. 

Be sure to keep in mind that finish times vary by variety and growing 

environment. 

As a general rule for many perennials, schedule delivery of your 

spring order in time to allow 6-10 weeks of growing time for 1-gal 

containers in a cool 50-60°F greenhouse. If plants will be grown 

outdoors with no frost protection, schedule delivery after risk of hard 

frost has passed as it is important to keep plants from freezing. 

What to do when your plants arrive 

Step 1: Open the Boxes 

When your order arrives, it is important to open all of the boxes and 

transplant all of the roots as soon as possible. Be sure to have plant 

labels on hand when potting to ensure correct identification. If you 

are not able to transplant the roots immediately, they may be stored 

in a cool (35-40°F) area for a limited time. 

Step 2: Inspect the Roots 

When you open the boxes, check the condition of the bare root 

plants. They should be firm, relatively dry, and typically are light 

brown in color. Since some bare root plants may have been stored 

in freezers where humidity is present, light surface mold may 

appear on some roots. It is not harmful to the plant and typically 

disappears once the boxes are opened and good air circulation is 

provided. It is not necessary to spray them with fungicide or remove 

the surface mold, though some customers prefer to do so. 

If any roots are still frozen, allow them to thaw slowly in a cool (40- 

50°F) room before handling. Do not put them immediately into a 

warm greenhouse. If the roots are dry, soak them in a tub of water 

containing a small amount of soluble fertilizer for one hour before 

potting. This will help the plants get established more quickly. 

If you are concerned about the condition of the plants in your 

shipment, contact your sales representative or broker or Walters 

Gardens, Inc. immediately so the issue can be resolved quickly. 

Step 3: Determine Planting Order 

The highest priority for transplanting bare root perennials should be 

given to all evergreen types such as Iberis, Lavandula, and Phlox 

subulata. Since their foliage is evergreen, these types of perennials 

can dessicate more quickly if left exposed. Those perennials which 

have thick, fleshy roots can typically be held over a bit longer before 

planting. However, remember to pot up all of your bare root material 

as soon as possible after receipt. 

Step 4: When You’ve Finished Planting 

We highly recommend that you apply a broad spectrum fungicide 

drench at the time of transplant to prevent crown and root rots. This 

is an important step that may take time now, but will save you time 

and money in the long run. After the drench has been applied, move 

the newly potted plants into a cool 50-60°F location with high light 

levels. Leave them there until roots have been established, and then 

raise the temperature slightly or move them to a warmer 

greenhouse to encourage top growth. 


Bare Root 

General Culture Guidelines for Bare Root Perennials 

The cultural information presented here is intended to give you 

general guidelines on how to grow bare root perennials. More 

specific cultural guidelines for special categories of perennials can 

be found on p. 22-28. In addition, a wealth of growing information is 

available on our website, www.WaltersGardens.com. Cultural sheets 

are provided for most genera, especially those that are more of a 

challenge to grow. Direction to the Culture Sheets portion of our 

website can be found under the Grower’s Corner section, or in the 

tab at the bottom of an individual plant page. 

Recommended Pot Sizes 

#1 Grade Plants — Most finish best in 1-gal containers, though 

some varieties such as Hibiscus are large enough to pot in 3-gal 

containers. 

#2 Grade Plants — Can be finished in 1-qt or trade 1-gal containers. 

#3 Grade Plants — Can be finished in 1-qt or trade 1-gal containers. 

Growing Media 

We suggest potting up your new perennial liners in a well-drained 

potting mix for optimum growth. A number of excellent bark or peatbased, 

soilless commercial mixes are available. Aim for a soil pH 

of 5.5-6.2 and an irrigation water pH of 5.4-7.0 for best results. For 

moisture loving plants, use growing media with little to no bark that 

will hold more moisture. Using a larger pot size will also keep the 

plants from drying out so quickly. 

Light and Temperature 

For optimum rooting, most perennials should be planted in full sun. 

For shade-loving plants such as ferns, hostas, Astilbe, and Dicentra, 

50-70% shade is recommended. 

When potting plants up in spring, be sure to keep the temperature 

above freezing. Cold, wet conditions may cause plants to decline 

or rot. Most perennials prefer to be grown at 50-55°F for 10-14 days 

after potting to promote root growth and then grown at 55-60°F 

until finished. Lower temperatures may be used to delay or suspend 

growth, while warmer temperatures generally help to accelerate 

growth. 

Bare Root Perennials to Grow Cool: Achillea, Amsonia, Astilbe, 

Artemesia, Baptisia, Clematis, Dicentra, Euphorbia, Irises, Lavandula, 

Nepeta, Paeonia, Papaver, Phlox subulata, and Salvia. See the 

Grower’s Reference Chart on p. 29 for a complete list. 

Bare Root Perennials to Grow Warm: Coreopsis, Crocosmia, 

Gypsophila, Hibiscus, Perovskia, Phlox paniculata, Rudbeckia, and 

Yucca. See the Grower’s Reference Chart on p. 29 for a complete list. 

Watering 

After potting up your bare root plants, water them in thoroughly to 

eliminate air pockets. Most bare root perennials benefit from being 

kept on the drier side initially because they are unable to absorb 

much moisture at this stage. The bare root plants need to develop 

feeder roots, and keeping them dry forces them to seek moisture, 

thereby initiating root growth. 

It is best to water early in the day so that the foliage will have a 

chance to dry out before the sun sets and the temperatures dip. 

This will help to avoid foliar diseases. 

Recommended 

Planting Depth 

Hemerocallis 

(Daylily) 


Hosta 

Allium 

(Ornamental Onion) 

Salvia 

(Perennial Salvia) 

Veronica 

(Spike Speedwell)

Bare Root 

When watering perennials with pubescent foliage, remember that 

water tends to collect in the center of the plant, causing crown rot. 

It is best to water pubescent and mildew-prone perennials early in 

the morning so they have plenty of time to dry out during the day. 

Monitoring Moisture Levels 

Some bare root perennials prefer to be grown slightly dry. Plant 

them in a very well-drained growing media, water them in, and 

then water sparingly thereafter. Perennials that prefer to be grown 

dry include: Amsonia, Artemisia, Euphorbia, Gypsophila, Iberis, 

Lavandula, Nepeta, Penstemon, Perovskia, Platycodon, Salvia, 

Sedum, and Yucca. 

Other bare root perennials prefer to be grown with consistent 

moisture levels. Their foliage tends to scorch and grow slowly if 

they do not receive enough moisture. Grow these plants moist: 

Astilbe, Dicentra, Hibiscus, Iris (Japanese, Louisiana, and Siberian), 

Polygonatum, and Tradescantia. 

Fertilizing 

When bare root plants are first potted up, they are not able to 

absorb fertilizer until they have established some feeder roots. Wait 

to fertilize newly potted plants until they show some foliage growth, 

approximately 4-6 inches for daylilies and other leafy perennials. 

Once the bare root plants are actively growing, they can be 

fertilized. Most growers use water soluble or slow release fertilizers 

or a combination thereof. In general, most perennials benefit from 

20-10-20 water soluble fertilizer at a rate of 50-150 ppm Nitrogen at 

every watering. 

To prevent salt build-up in the soil, avoid using slow-release fertilizer 

in the soil until the weather begins to warm up in spring (around 

April 1st in the north). Very little fertilizer is released before that 

time when it is cold and cloudy. Always follow the manufacturer’s 

recommendations when using fertilizer. 

When potting up bare root plants in fall, do not use slow-release 

fertilizer. Doing so will promote soft growth which could result in 

severe die-back or death if exposed to freezing conditions. 

When potting plants in spring, if you are using a slow release 

fertilizer, it is best to incorporate it into the growing media at a rate 

of 3/4 to 1 pound per cubic yard. Alternatively, you may top dress the 

pots taking care not to apply the fertilizer directly to the crown of 

the plants. 

perennials, such as Hibiscus, prefer to have more space than others 

when being grown to their finished size. In general, the more space 

you can give plants to finish, the better their finished appearance 

will be. 

Air Circulation 

Adequate air circulation is essential to avoiding disease issues when 

growing perennials. This is especially important for mildew-prone 

varieties such as Phlox paniculata and Pulmonaria. Be sure to 

space plants well so the air has room to circulate around them. Use 

fans or other ventilation if necessary. 

Weed Control 

We do our best to deliver clean, weed-free stock to our customers. 

However, weeds are opportunists that will grow wherever they 

possibly can. Some herbicides can be used successfully on certain 

crops, but it is safest to pull weeds on a weekly basis before they 

grow large and establish their roots. 

Forcing Bare Root Perennials 

Since most bare root material that is shipped from Walters Gardens, 

Inc. in spring in a dormant state has already been vernalized, it can 

be forced easily for sale anytime you’d like as long as the required 

day length is met. Supplemental lighting may be required to 

achieve satisfactory results. Alternatively, plants can be allowed 

to come into flower naturally. The amount of time it takes to bring 

plants into bloom varies widely by genus. 

Plant Placement 

The growing surface you select should have good drainage so that 

plants never sit in water for an extended period. Landscape fabric 

can be used for weed prevention. Be sure to space plants well 

and use fans if necessary to provide good air circulation. Some 


Plugs / Liners 

Of our wide selection of over 1,000 perennials, approximately half of our product line is offered in plug form. Depending on the needs of the plant, 

it may be grown in an Elle Plug or a traditional loose fill plug tray. A full range of plug sizes, including 20, 30, 72, and 128 count trays, is available 

to finish in your gallon, quart, or 6-pack sized containers. See timing chart on p. 3 for additional details. 

Sizes 

12” 

11” 

10” 

9” 

8” 

7” 

6” 

5” 

4” 

3” 

2” 

1” 

128ct Plug 

(Elle) 

72ct Plug 

(Elle) 

30ct Plug 

(Elle) 

30ct Plug 

(Deep Cell) 

20ct Plug 

(Elle) 

20ct Plug 

(Deep Cell) 

10 | Walters Gardens


Scheduling delivery of your plug perennials 

As a grower, you know that timing is everything. Sometimes it 

takes a little experimenting to figure out what works best in your 

specific climate. To help take the guesswork out of finishing your 

plug perennials, we offer you some guidelines in our timing chart on 

p. 3. Be sure to keep in mind that finish times vary by variety and 

growing environment. 

As a general rule for many perennials, schedule delivery of your spring 

order in time to allow 6-10 weeks of growing time for 20 or 30ct plugs 

finishing in 1-gal containers and 4-6 weeks for 72ct plugs finishing 

in quarts (see timing chart on p. 3 for details.) If plants will be grown 

outdoors with no frost protection, schedule delivery after risk of hard 

frost has passed. It is important to keep plants from freezing. 

What to do when your plants arrive 

Step 1: Open the Boxes 

When your plug order arrives, it is important to open all of the boxes 

and transplant all of the plugs as soon as possible. Be sure to have 

plant labels on hand when potting to ensure correct identification. If 

you are not able to transplant the plugs immediately, they may be 

stored in a cool area for a limited time. 

Step 2: Inspect the Plugs 

When you open the boxes, check the condition of the plugs. 

Depending on the time of year and the variety, the plants may 

be dormant or fully leafed out. If any plugs have frozen during 

shipment, allow them to thaw slowly in a cool (40-50°F) room before 

handling. Do not put them immediately into a warm greenhouse. 

We strive to ship our plugs with sufficient moisture to last through 

shipping. However, if any plugs appear dry they should be watered 

immediately. Since all of our plugs contain a wetting agent in the 

soil, they should re-wet easily. 

If you are concerned about the condition of the plants in your 

shipment, contact your sales representative or broker or Walters 

Gardens immediately so the issue can be resolved quickly. 

Step 3: Determine Planting Order 

If there are both bare root and plug perennials included in your 

perennial shipment, the highest priority for transplanting should be 

the bare root varieties. 

Once all of your bare root plants are potted up, you should begin 

transplanting your plug perennials beginning with the smallest sized 

plugs. 

If you plan to hold over your plugs for a short period of time before 

transplanting them, be sure to check them regularly to ensure they 

are kept evenly moist. Never let the plugs dry out. 

Step 4: When You’re Finished Planting 

We highly recommend that you apply a broad spectrum fungicide 

drench at the time of transplant to prevent crown and root rots. 

This is an important step that may take time now, but will save you 

time and money in the long run. After the drench has been applied, 

move the newly potted plants into a cool 55-60°F location with high 

light levels.Leave them there until roots have been established, and 

then raise the temperature to 60-65°F or move them to a warmer 

greenhouse to encourage top growth. 



General Culture Guidelines for Plug Perennials 

The cultural information presented here is intended to give you 

general guidelines on how to grow plug perennials. More specific 

cultural guidelines for special categories of perennials can be found 

on p. 22-28. 

In addition, a wealth of growing information is available on our 

website, www.WaltersGardens.com. Cultural Sheets are provided for 

most genera, especially those that are more of a challenge to grow. 

Direction to the Culture Sheets portion of our website can be found 

under the Grower’s Corner section, or in the tab at the bottom of an 

individual plant page. 

Recommended Pot Sizes 

20 and 30ct Plugs — Most finish best in 1-gal containers, though 

smaller varieties such as miniature hostas may work better in quarts. 

72ct Plugs — Can be finished in trade 1-gal, 1-qt, or 6 pack containers. 

Transplanting 

When transplanting Elle Plugs, it is not necessary to remove the 

paper sleeve since it will naturally degrade over time. The thinner 

Elle Plug paper that is being used now degrades more quickly than 

when the technology was new. However, some customers are more 

comfortable removing the paper. This is acceptable only if it will not 

harm the root structure of the plant. 

As a general rule, perennials grown in traditional or Elle Plugs should 

be potted up with the crown at the same soil level it was growing 

in the plug. The Elle Plug paper should not stick up above the soil 

surface after transplanted. Elle Plugs should be thoroughly watered 

prior to transplanting. 


Most Plug Perennials, 

such as the Hosta 

pictured here, should be 

planted even with the soil 

level, or just a bit below 

Growing Media 

We suggest potting up your new perennial liners in a well-drained 

potting mix for optimum growth. A number of excellent bark or peatbased, 

soilless commercial mixes are available. Aim for a soil pH 

of 5.5-6.2 and an irrigation water pH of 5.4-7.0 for best results. For 

moisture loving plants, use growing media with little to no bark that 

will hold more moisture. Using a larger pot size will also keep the 

plants from drying out so quickly. 

Light and Temperature 

For optimum rooting, most perennials should be planted in full sun. 

For shade-loving plants such as ferns and hostas, 50-70% shade is 

recommended. 

When potting plants up in spring, be sure to keep the temperature 

above freezing. Cold, wet conditions may cause plants to decline 

or rot. Most perennials prefer to be grown at 48-55°F for 10-14 days 

after potting to promote root growth and then grown at 55-60°F 

until finished. Lower temperatures may be used to delay or suspend 

growth, while warmer temperatures generally help to accelerate 

growth. 

Plug Perennials to Grow Cool: Aquilegia, Brunnera, Delphinium, 

Dicentra, Digitalis, Geranium, Grass-cool season, Helleborus, 

Heuchera, Heucherella, Leucanthemum, and Lupinus. See the 

Grower’s Reference Chart on p. 29 for a complete list. 

Plug Perennials to Grow Warm: Buddleia, Campanula, Coreopsis, 

Echinacea, Grasses-warm season, Gypsophila, Heliopsis, Perovskia, 

Rudbeckia, non-hardy Succulents and Tropicals. See the Grower’s 

Reference Chart on p. 29 for a complete list. 

Watering 

After potting up your plug perennials, water them in thoroughly to 

eliminate air pockets. Initially, Elle Plug perennials benefit from extra 

watering to help the plug absorb moisture. It is best to water early 

in the day so that the foliage will have a chance to dry out before 

the sun sets and the temperatures dip. This will help to avoid foliar 

diseases. 

When watering perennials with pubescent foliage, remember that 

water tends to collect in the center of the plant, causing crown rot. 

It is best to water pubescent and mildew-prone perennials early in 

the morning so they have plenty of time to dry out during the day. 



Once the plants are actively growing, they can be fertilized. 

Most growers use water soluble or slow release fertilizers or a 

combination thereof. In general, most perennials benefit from 

20-10-20 water soluble fertilizer at a rate of 50-150 ppm Nitrogen at 

every watering.To prevent salt build-up in the soil, avoid using slowrelease 

fertilizer in the soil until the weather begins to warm up in 

spring (around April 1st in the north). Very little fertilizer is released 

before that time when it is cold and cloudy. Always follow the 

manufacturer’s recommendations when using fertilizer. 

When potting up plugs in fall, do not use slow-release fertilizer. 

Doing so will promote soft growth which could result in severe dieback 

or death if exposed to freezing conditions. 

For the most 

accurate snapshot 

of a container’s 

moisture level, 

check the drainage 

holes at it’s base. 

Monitoring Moisture Levels 

When growing perennials in a polyhouse, moisture levels can 

vary depending on location and exposure. Areas that are prone to 

drying out, such as those along sidewalks or near fans, should be 

monitored closely. Perennials such as Dianthus and ornamental 

grasses which prefer drier conditions would be good candidates for 

such dry areas of the polyhouse. 

Do not rely upon surface moisture to determine when it is time to 

water. Instead, check the drain hole in the bottom of the container 

for moisture. Most perennials prefer when the soil dries down a bit 

between waterings. 

Some plug perennials prefer to be grown slightly dry. Plant them in 

a very well-drained growing media, water them in, and then water 

sparingly thereafter. Grow these plants slightly dry: Aquilegia, 

Asclepias tuberosa, Corydalis, Delosperma, Dianthus, Echinacea, 

Epimedium, Gaillardia, Heuchera, Lupinus, Nepeta, Oenothera, 

Perovskia, Stachys, Thymus, and Yucca. See the Grower’s Reference 

Chart on p. 29 for a complete list. 

Other plug perennials prefer to have consistent moisture levels. 

Their foliage tends to scorch and grow slowly if they do not receive 

enough moisture. Grow these plants moist: Cimicifuga, Dicentra 

(except ‘Fire Island’ and ‘Pink Diamonds’), Galium, Ligularia, Lobelia, 

Primula, Pulmonaria, Tiarella, and Trollius. See the Grower’s 

Reference Chart on p. 29 for a complete list. 

Fertilizing 

When plugs are first potted up, they are not able to absorb fertilizer 

until they have established some feeder roots. Wait to fertilize newly 

potted plants until they show some foliage growth. 

Plant Placement 

The growing surface you select should have good drainage so that 

plants never sit in water for an extended period. 

Landscape fabric can be used for weed prevention. Be sure to space 

plants well and use fans if necessary to provide good air circulation. 

Some perennials, such as Hibiscus, prefer to have more space 

than others when being grown to their finished size. In general, the 

more space you can give plants to finish, the better their finished 

appearance will be. 

Air Circulation 

Adequate air circulation is essential to avoiding disease issues when 

growing perennials. This is especially important for mildew-prone 

varieties such as Phlox paniculata and Pulmonaria. Be sure to space 

plants well so the air has room to circulate around them. Use fans or 

other ventilation if necessary. 

Weed Control 

We do our best to deliver clean, weed-free stock to our customers. 

However, weeds are opportunists that will grow wherever they 

possibly can. Some herbicides can be used successfully on certain 

crops, but it is safest to pull weeds on a weekly basis before they 

grow large and establish their roots. 

Forcing Plug Perennials 

When purchasing fresh material, plants should be bulked up and 

vernalized over winter. Many perennials require vernalization to 

bloom, while others may benefit from but not require vernalization. 

Few do not require any vernalization to bloom. When receiving 

plugs in spring from Walters Gardens, they will already have been 

vernalized for the necessary amount of time in order to flower. Once 

vernalized, plug perennials can be bulked and forced easily for 

sale anytime you’d like as long as the required day length is met. 

Alternatively, they can be allowed to come into flower naturally. 


Culture Guide 

Five Recommendations for Growers 

If you’re struggling with a certain crop or just starting out and need some good pointers, here are the top five things growers need to watch 

for when finishing perennials. 

1. Not all perennials are alike. If you plan to grow many different kinds of perennials, you’ll need multiple kinds of growing environments 

in which to grow them. See p. 22-28 for cultural recommendations for specialized plants. 

2. Many perennials benefit from planting the summer or fall prior to the season of sales. Often, you can start with a smaller plug and 

yield bigger results by starting plants this way. See p. 38-39 for details. 

3. Growing media is crucial. Know your soil and test it regularly for pH and EC levels. Choose the right growing media for each type of 

perennial you are growing, whether it’s one that holds a lot of moisture for water loving plants or one that drains freely for those that 

like it on the dry side. 

4. Some top selling perennials with dark foliage, such as Hibiscus, need to be grown outdoors in order for the optimum color to be 

developed. Creating the proper growing environment goes a long way towards growing the best quality finished perennials. 

5. Many perennials, especially those that were started the summer or fall prior, can be forced into bloom for early spring sales. Keep in 

mind however that most will require supplemental lighting and heat to force into bloom out of their natural cycle. 

Watering Practices 

Water quality is very important in perennial production. It is one of 

the foundations of growing a quality crop of perennials. It is wise 

to have your water source tested regularly for pH, salt levels, and 

alkalinity. Perennials grow best when water is slightly acidic. You 

may need to make adjustments to your water supply. If it is too 

alkaline, you may need to inject acid into the water or use an acidic 

fertilizer. If it is too acidic, you may need to inject a basic fertilizer. 

When plants need water, it is best to water them well all the way 

through the pots and then allow them to dry slightly between 

irrigations. This will promote root growth to the bottom of the pots. If 

plants are watered lightly but more frequently, they tend to produce 

more surface roots and have a difficult time pushing roots to the 

bottom of the pots. It is best to water your perennials early in the 

morning to allow plenty of time for the foliage to dry before evening. 

This will help to prevent disease issues such as root and crown rots. 

An average growing media used for perennials contains a balanced 

blend of peat, perlite, and bark. However, if you plan to use overhead 

watering as the primary irrigation source, use a soil mix that is very 

well-drained, containing a high concentration of bark and perlite and 

less peat. An exception would be plants that require consistently 

moist soil—those should be potted in a peat/perlite media with 

minimal bark. When overhead watering, it is very important to 

monitor pH and EC levels to ensure proper fertility since this practice 

tends to leach fertilizer out of the soil. 

Certain crops, especially those with pubescent leaves like Stachys 

or Pulmonaria, perform better if drip or sub-irrigation is used. This 

allows the foliage to stay dry and lessens the chances for rot. Be 

sure to water such crops in the morning to allow plants to dry 

thoroughly before nightfall. 

When growing perennials that require consistent moisture in 

outdoor growing facilities, it is important to monitor moisture levels 

very closely. Such crops as Hibiscus may need to be watered 

several times per day. Drip irrigation works best in situations like this 

since it can be set on a timer or turned on any time of day without 

getting the foliage wet, preventing foliar diseases. 


Culture Guide 

Water by Number 

Proper watering techniques can be difficult to teach to new 

employees, especially when there is a language barrier. Tagawa 

Greenhouse in Colorado developed a watering system that consists 

of five levels from extremely dry (level 1) to wet (level 5) and is based 

on visual and tactile clues for the worker. We have adapted their 

system for our customers growing finished product, shown at right. 

The primary watering range for most perennials is 2-4, meaning 

they are watered up to a level 4 and allowed to dry down to a level 

2 before they are watered again. Perennials that prefer drier soils 

Levels 

Level 1 - Extremely Dry 

• Soil is light brown all the way through, dry to the touch, and separates easily from the edge of the pot. 

• Soil will not stick together if pinched between fingers and may become hard and crumbly. 

• Soil is difficult to re-wet even with a wetting agent. 

• Plants may begin to wilt. 

• Container is very lightweight. 

Level 2 - Slightly Dry 

• Soil is light brown at the top and slightly darker brown further down in the pot. 

• Soil is fairly dry to the touch. 

• Soil will stick together if pinched between fingers but falls apart easily. 

• Container is lightweight. 

are watered up to a level 3 and dried down to a level 2. Conversely, 

perennials that prefer more moist soils are typically watered up to 

a level 4 and dried down to a level 3. Few perennials can handle the 

extremes of levels 1 and 5. 

Below is a visual and descriptive account of each of the five 

watering levels. We recommend that you adapt this system to your 

own nursery, using your own plants, and post it in a prominent 

location for your workers to reference on a regular basis. 

Level 3 - Average 

• Soil is medium brown most of the way through the pot but darker brown at the very bottom. 

• Soil is slightly damp to the touch. 

• Soil will stick together if pinched between fingers. 

• Pots around the edges of the crop block dry out quicker and should be monitored for moisture. 

• Container is of moderate weight but does not drip water. 

Level 4 - Moist 

• Soil is dark brown all the way through the pot. 

• Soil feels moist to the touch. 

• Some water can be squeezed from the pot. 

• Container is slightly heavy but does not drip much water. 

Level 5 - Wet 

• Soil is dark brown to black all the way through the pot because it is fully saturated. 

• Soil feels wet to the touch. 

• Water drips from the pot when you pick it up. 

• Container is very heavy and drips a lot of water. 


Culture Guide 

Onsite Soil Testing 

In addition to water quality, onsite soil testing is one of the 

foundations of growing a quality crop of perennials. Surprisingly, 

it is often overlooked by growers. Investing in onsite soil testing 

is well worth the effort and minimal expense as it helps to prevent 

nutritional deficiencies and grow more vigorous, healthier, pest and 

disease resistant crops. We recommend that you invest in a good 

quality pH/EC soil testing kit. They are readily available online for 

approximately $200-$300. 

There are several methods of testing soil, but the one we 

recommend is called the pour thru method. You will notice the EC 

rates given in this guide specify they are using this method. You will 

also find recommended pH and EC rates on our cultural sheets on 

www.WaltersGardens.com 

There are seven basic steps to testing soil for pH and EC levels 

using the pour through method, as defined by North Carolina State 

University’s Floriculture Research department. 

1. Irrigate the plants you are going to test one hour before testing 

begins. Make sure the growing media is completely saturated. 

2. Put a saucer or something to catch the water under the pots right 

before you start the test. 

3. Pour enough distilled water on the potted plants to get 50ml of 

leachate (the water that drains through the container). For a one 

gallon pot, this is typically 150ml of distilled water. Water must be 

distilled or deionized to obtain accurate readings. 

4. Collect the leachate in a clean container so you can measure its 

pH and EC. 

5. Before testing the leachate, calibrate your pH and EC meters. 

Skipping this step may lead to inaccurate readings. 

6. Measure the pH and EC of your samples as soon as possible after 

they are collected. 

7. Make adjustments to the pH and EC levels of your soil as needed. 

NC State University is an excellent source of information about soil 

testing. Visit their website: www.ces.ncsu.edu/depts/hort/floriculture 

Tips for Successful PGR Applications 

Some perennials benefit from applications of growth regulators to 

ensure the highest quality crop. While ideal growing conditions and 

spacing go a long way to improve quality, it is not always possible 

to have the best environment for every crop and some plants that 

are naturally quite tall can benefit from PGR applications even when 

grown in the very best possible situation. Here are some tips on 

applying growth regulators and rate suggestions for starting with 

on the genera that you might find needing some control on a more 

frequent basis. Keep in mind that these rates are just suggestions, 

and will vary based on your regional location, environment and even 

the water quality in your operation. 

• Apply foliar PGR applications early in the morning (or on a cloudy 

day) for best results – this allows them to dry the slowest and 

gives the most uptake. If in a greenhouse with retractable shade 

curtains, you can also pull the shade on a sunny day in a pinch. 

You can increase uptake by running a LIGHT MIST of water over 

the crop when it is almost dry from the application – not enough 

to rinse the chemical off, just enough to rewet the foliage. 

• Uniconazole (Sumagic/Concise) and Paclobutrazol (Bonzi/Piccolo) 

require stem contact for best absorption. 

• Familiarize yourself with the labels, and make sure to use a 

surfactant if suggested on the label – for example, Configure has 

the best efficacy if applied with a surfactant. Capsil is a good 

example, the rate typically used with Capsil is 6oz/100gals. Apply 

volumes based on label suggestions. Some PGRs require only a 

light spray (ie. Cycocel) whereas others require a heavier spray. 

• Some PGRs (Dikegulac Sodium, Fascination/Fresco, Cycocel, 

Florel) may cause either yellowing or a halo – this is normal and 

plants will outgrow it. 

• When drenching, try to apply when soil has been allowed to dry 

slightly so you get the most uptake of the chemical, and then be 

careful not to apply so much water as to leach the chemical out 

for the 7-10 days. 

• Everyone has their own method, but the “safest” way (and often 

the best results) is to layer lighter spray applications on as 

needed rather than a one-time punch of a drench or higher rate 

spray. 

• There is a lot of good information out there (less so on 

perennials, but getting better!). A great resource is the annually 

published Grower Talks PGR guide – one on annuals, one on 

perennials. Start there and make adjustments as needed based 

on your crop and growing conditions. 


Plant Growth Regulator (PGR) Recommendations 

Genus 

Hardy Perennials 

Plant Growth 

Regulator (PGR) 

Rate 

Achillea Daminozoide 2500 ppm 

Daminozide + Uniconazole 

Uniconazole 

Configure 

2000 + 3 ppm 

7-15 ppm 

2500-5000 ppm 

Agastache Daminozide 2500-5000 ppm 

Daminozide + Chlormequat 

Chloride 

Paclobutrazol 

Uniconazole 

Configure 

2500-5000 + 1000-1500 

ppm 

30-60 ppm 

5-10 ppm 

300-500 ppm 

Alcea Paclobutrazol 5-15 ppm 

Paclobutrazol 

Uniconazole 

3-6 ppm drench 

2.5-5 ppm 

Amsonia Paclobutrazol 15 ppm 

Uniconazole 

Uniconazole 

5-10 ppm 

1 ppm drench 

Anemone Daminozide + Uniconazole 2000 + 3 ppm 

Aquilegia Daminozide 1500-2500 ppm 


Uniconazole 

1875 + 3 ppm 

5-15 ppm 

Arabis Daminozide 2500 ppm 

Notes 

Culture Guide 

PGRs may need to be applied multiple times to get good 

control. 

Apply PGRs as sprays early, before elongation has 

occurred. If elongation has already occurred, best 

control is through the Paclobutrazol drench. 

Apply just as flower stems are beginning to elongate. 

Not required on some varieties. 

Artemisia Daminozide 5000 ppm Growing cool and dry will reduce the need for PGR. 


Chloride 

Paclobutrazol 

5000 + 1500 ppm 

40-50 ppm 

Aruncus Uniconazole 5 ppm 

Asclepias Daminozide 3750-5000 ppm 

Uniconazole 

5-10 ppm 

Aster Daminozide 2500-5000 ppm Make first application 5-7 days after pinching. 

Paclobutrazol 

30-50 ppm 


Culture Guide 


Genus 


Plant Growth 


Rate 

Astilbe Daminozide 2500-5000 ppm Apply PGR when flower stem appears above foliage. 


Paclobutrazol 

Uniconazole 

2000 + 3 ppm 

15-30 ppm 

5-10 ppm 

Baptisia Paclobutrazol 6-10 ppm drench 

Uniconazole 

Uniconazole 

1 ppm drench 

5-15 ppm 

Notes 

Growing cool is the best height control. Make first PGR 

applications early in the crop, when shoots are just a few 

inches tall. 

Brunnera Daminozide 2500 ppm If toning is required, often not needed. 

Uniconazole 

5 ppm 

Buddleia Paclobutrazol 6 ppm drench Begin PGR applications 1-2 weeks after pinching. 

Uniconazole 

5-15 ppm 

Campanula Daminozide 2500-3750 ppm 

Paclobutrazol 

Uniconazole 

10-30 ppm 

2-5 ppm 

Clematis (Herbaceous) Uniconazole 5-10 ppm 

Coreopsis Daminozide 2500-5000 ppm 


Uniconazole 

2000 + 3 ppm 

5-10 ppm 

Apply just as flower stems are beginning to elongate. 

Compact varieties will need little to no PGR, start on 

these with 2500 ppm Daminozide. 

Delphinium Paclobutrazol 30 ppm Apply when flower stems grow above foliage. 

Uniconazole 

5 ppm 

Dianthus Daminozide + Uniconazole 2000 + 3 ppm Typically not needed if grown cool. 

Dicentra Daminozide 2500 ppm 

Digitalis Ancimidol 25 ppm 

Daminozide 

Uniconazole 

2500 ppm 

5 ppm 

Echinacea Daminozide 2500 ppm 


Uniconazole 

Uniconazole 

2000-2500 + 3-5 ppm 

5 ppm 

1 ppm drench 

Euphorbia Flurprimidol 45 ppm 

Paclobutrazol 

Uniconazole 

30 ppm 

5 ppm


Genus 

Plant Growth 


Rate 

Gaillardia Daminozide 2500-5000 


Chloride 

Daminozide + Paclobutrazol 


2500-3750 + 1000 ppm 

2500-3750 + 15 ppm 

2000-2500 + 3-5 ppm 

Gaura Daminozide 2500 ppm 

Uniconazole 

5 ppm 

Geranium Daminozide + Uniconazole 2000 + 3 ppm 

Uniconazole 

5 ppm 

Notes 

Culture Guide 

Geum Paclobutrazol 30 ppm Apply as flower stems grow above foliage. 

Uniconazole 

5 ppm 

Heliopsis Daminozide 2500 ppm 

Uniconazole 

5-10 ppm 

Hemerocallis Uniconazole 1 ppm drench 

Heuchera Uniconazole 5-10 ppm Typically not needed if grown under ideal conditions. 

Heucherella Uniconazole 5-10 ppm Typically not needed if grown under ideal conditions. 

Hibiscus 


Chloride 

Uniconazole 

Paclobutrazol 

3750 + 1000 ppm Apply PGRs about 5 days after a pinch. 

2.5-15 ppm 

1 ppm drench 

Hosta Daminozide 2500 ppm 

Uniconazole 

Uniconazole 

5 ppm 

1 ppm drench 

Iberis Paclobutrazol 15 ppm 

Uniconazole 

2.5 ppm 

Knautia Daminozide 2500 ppm 

Paclobutrazol 

Uniconazole 

30 ppm 

5 ppm 

Kniphofia Paclobutrazol 30-45 ppm 

Uniconazole 

5-7.5 ppm 

Lavandula Uniconazole 5 ppm 

Leucanthemum Uniconazole 5-7.5 ppm 

Liatris Uniconazole 5.10 ppm 

Be aware of what size class of hosta you are growing. 

Mini, small, and unvernalized hosta will not typically 

need any PGR. 


Culture Guide 


Genus 

Plant Growth 


Rate 

Lobelia Ancimidol 25 ppm 

Daminozide 

Uniconazole 

2500 ppm 

5 ppm 

Lupinus Daminozide 2500 ppm 


Paclobutrazol 

2000 + 3 ppm 

20 ppm 

Malva Paclobutrazol 15 ppm 

Uniconazole 

2.5 ppm 

Monarda Daminozide + Uniconazole 2000 + 3 ppm 

Nepeta Paclobutrazol 30 ppm 

Uniconazole 

5 ppm 

Oenothera Uniconazole 5-10 ppm 

Papaver Daminozide 2500 ppm 

Penstemon Daminozide 2500 ppm 

Uniconazole 

5-10 ppm 

Perovskia Daminozide 2500 ppm 


Uniconazole 

2000 + 3 ppm 

5-10 ppm 

Phlox (Tall Garden) Paclobutrazol 45 ppm 

Uniconazole 

10 ppm 

Platycodon Daminozide 2500 ppm 

Uniconazole 

5 ppm 

Rudbeckia Daminozide 2000 ppm 

Uniconazole 

3 ppm 

Salvia Daminozide 2500 ppm 

Uniconazole 

5-10 ppm 

Scabiosa Daminozide 2500 ppm 

Paclobutrazol 

Uniconazole 

30 ppm 

5 ppm 

Sedum Daminozide 2500-5000 ppm 

Paclobutrazol 

Uniconazole 

20-30 ppm 

5-10 ppm 

Spigelia Uniconazole 5-10 ppm PGR not typically needed if grown under ideal conditions. 

Stokesia 


Chloride 

2000 + 1000 ppm 

Notes 



Genus 

Plant Growth 


Rate 

Notes 

Tiarella Uniconazole 5 ppm Typically not needed. 

Tradescantia 

Veronica Uniconazole 5-10 ppm 

Viola Daminozide 2500 ppm 

Grasses & Sedges 

Best growth control is growing in cool temperatures. 

Calamagrostis Flurprimidol 10 ppm Make first application when plants are 6-12" tall. 

Paclobutrazol 

Uniconazole 

10 ppm 

1 ppm drench 

Miscanthus Flurprimidol 10 ppm 

Paclobutrazol 

Uniconazole 

10 ppm 

2 ppm 

Panicum Flurprimidol 10 ppm 

Paclobutrazol 

Uniconazole 

10 ppm 

2 ppm 

Pennisetum Flurprimidol 10 ppm 

Tropicals 

Paclobutrazol 

Uniconazole 

10 ppm 

2 ppm 

Digiplexis Uniconazole 10 ppm Apply PGRs just as flower spikes are starting to elongate. 

Uniconazole 

1 ppm drench 

Culture Guide 


Culture Guide 

Culture Recommendations for Specialized Plants 

Astilbe 

Plant in 1-gal containers with the eyes just at or slightly below the 

soil surface. 

Begin growing plants cool at 50-55°F for the first 10-14 days. After 

that, increase the temperature to 55-60°F to speed flowering or 

lower temperature to delay flowering. 

The most critical growing factor for Astilbe is water. Increase 

watering as the foliage emerges and plumes mature. Plants should 

never be allowed to dry out. If the margins of the leaves turn brown 

and crispy, the plants are not being kept moist enough. Avoid 

watering after mid-afternoon. 

Astilbes are moderate feeders. We recommend a constant liquid 

feed of 50-100ppm N. 

Because they are sensitive to high salts, the plants may experience 

root injury and become scorched if the soluble salt levels are 

allowed to build up. We recommend an EC of 1.5-2.0 using the pour 

through method. 

• Use mouse bait when overwintering. 

• Plants should be shaded during periods of high light intensity. 

A 55% shade cloth is recommended in the north when 

temperatures reach 65-70°F. A heavier 70% shade cloth will be 

necessary in the south. 

Baptisia (False Indigo) 

The big concern with bare root Baptisia is that the roots will dry out 

since dry roots are almost always connected to poor performance. 

Fortunately, there are a few quick and easy steps that can be taken 

to ensure success in growing. 

First, plant your bare root Baptisia as soon as possible into a 

true 1-Gallon container or larger. If the roots are too large for the 

container you can trim them slightly right before potting. 

Planting depth is very important. The eyes should be planted right at 

the soil line so the crown is completely submerged. If the crown sits 

above the soil the roots will become significantly drier than if the 

crown is below and result in poorer performance. 

Due to the dense nature of the root system there is a probability 

that air gaps will form below the crown and surrounding roots when 

planting from bare root. Taking care to fill in between the roots when 

planting, as well as a thorough watering after planting will solve this 

concern. 

A porous peat based growing media or well drained bark are usually 

good choices. 

Despite heavy concerns over dry roots, Baptisias are not a thirsty 

plant. Once the roots are established, they require only low to 

moderate watering. 

Start cool at 55-60°F and provide high light levels with good air 

movement. 

Pinching is not necessary and has a good chance of removing or 

damaging the emerging flowers. Baptisia are vigorous growers, 

drenching with Bonzi at 6” tall will effectively control plant height. 


Baptisia plugs should be 

about 1/2” below the soil 

line. This will promote 

better eye development 

and more stems the 

following year. 

Clematis (Herbaceous, non-Vining) 

When most people think of Clematis they are usually thinking of 

the vining types, but bush Clematis are much easier to control in 

containers than their vining counterparts and have unique, bellshaped 

flowers that lend a very different look to the garden. 

Bush Clematis, or herbaceous 

clematis, are offered as bare root 

inputs and should be planted 

with the crown slightly below the 

soil line in late winter to spring. 

The bare root material will have 

received a vernalization in the 

fields, so no additional cold 

treatment is needed. 

In the landscape, bush Clematis 

benefits from either some 

perennial neighbors or an 

obelisk to help support the foliage. Likewise in containers, a trellis 

will help to maintain the upright form. 

High light levels will help to grow the highest quality plants. 


Culture Guide 

Echinacea (Coneflower) 

Walters Gardens begins to ship vegetatively propagated, actively 

growing Echinaceas in the beginning of April. Prior to April 1st, 

Echinacea are shipped in either a dormant or newly emerging state. 

If you do not have a heated greenhouse in which to keep them 

actively growing, schedule your delivery later in spring when night 

temperatures average 50-60°F and daytime temperatures average 

65-70°F. 

• High light intensities are required for best growth. 

• Echinaceas flower best under 14 hour days or a four hour night 

interruption between 10PM and 2AM. 

• Best performance comes in well-drained soil of moderate 

to slightly dry moisture. Allow the soil to dry down between 

waterings for best root growth. 

• Echinacea will become stunted and lack overall vigor if fertilizer 

and EC levels are too high. Use slightly acidic soil with an EC of 

1.5-2.0 using the pour through method for best results. 

Helleborus (Lenten Rose) 

Hellebores are a long crop, but worth the wait. We offer several 

different plug inputs that can be utilized at varying time of year. 

• 128ct plugs are the smallest and should be planted in late winter 

to early spring in the south, or early summer in northern regions, 

and can be sold green later the same season or overwintered 

for the following spring’s sales. Expect only 10-15% flowering 

that following spring, since they will have received only one 

vernalization. 

• 30ct plugs are a larger input and should be planted in late winter 

to early spring in the south, and in the late winter in the north. 

Follow similar timing as for the 128s, selling green plants later 

that summer or lightly flowering plants the following spring. 

• 20ct plugs are the largest plug size we offer and are available in 

both the fall and the spring. Fall planted 20cts bulk and develop 

roots well at that time of year since hellebore actively grow 

during the cooler months, and then will bloom at about 80% 

capacity the following spring. Spring planted 20cts have already 

received a second vernalization in the plug, so can be planted 

and sold the same season at about 80% flowering capacity. 

Hellebores are cold weather plants which are actively growing 

from late winter through spring. They stop growing in summer but 

resume growth again in the fall. Plants in production through the 

summer should be pushed tightly together to help maintain a cooler 

environment around the roots. Reflective aluminum shade cloth 

also helps to keep plants cooler during the summer months. 

When plants are actively growing, fertilize moderately with 100- 

150ppm N at every irrigation. Reduce to 75-150ppm N at every other 

irrigation in summer and mid-winter. 

Use a bark-based growing media with a slightly acidic pH of 5.8-6.4. 

In production, Hellebores prefer average moisture, and should be 

allowed to dry only slightly between waterings. In the garden, they 

are quite drought tolerant. 

Use a 50-75% shade cloth for this shade perennial during the 

summer months. 

Vernalization is required for flowering. Plants that are produced from 

tissue culture bloom about 85% after one vernalization compared to 

those produced from seed which bloom about 10-15%. All plants will 

bloom after the second vernalization. After the potted plants have 

been bulked up from spring through fall, vernalize them for up to 

8-10 weeks at 35-40°F and keep them cold until you want them to 

flower. Flowering often begins even in unheated greenhouses in the 

late winter, especially when temperatures are above 35°F. 

Hemerocallis (Daylilies) 

Daylilies are one of the most widely 

recognized perennials, are deer and 

rabbit resistant, and are very 

versatile in the landscape. 

Hardy from zones 3 to 9, they 

can be used throughout a wide 

range of garden conditions. 

Our daylilies are all grown in 

our bare root fields and roots 

are trimmed before shipping. 

Root pruning is preferable to 

cramming the roots into a pot, and 

will not result in any setback in 

growth. In many cases trimming will 

actually accelerate rooting in. 

Bare root divisions should be planted in 

well-drained media and watered in thoroughly. 

Hemerocallis prefer even moisture until established, but then can 

be allowed to dry down slightly between irrigations until bud set, at 

which point returning to consistent moisture application will improve 

flower quality. 

For the first few weeks after planting, daylilies do not require 

fertilizer. Once actively growing they are moderate feeders and will 

perform best under a constant liquid feed program of 75-125 ppm N. 

Too much fertilizer will encourage soft, weak growth. 

Late summer planting will result in bigger plants and more flowers. 

Allow at least 6-8 weeks to establish roots before temperatures 

drop consistently below freezing, and do not fertilize at this time. 

When overwintering, trim plants to 2 inches as late in the season as 

possible, as trimming too early will result in unwanted regrowth. 


Culture Guide 

Hibiscus (Culture for Spring Planting) 

• Pot up bare root Hibiscus immediately upon arrival. 

• Grow Hibiscus in full sun at 68°F or warmer constant 

temperature. Bare root plants can be grown colder outdoors. 

• Grow cultivars with purple foliage outdoors to achieve proper 

coloration. 

• Pinch top growth back once to 3-5 nodes. 

• Drench each pot with 1ppm Sumagic® one week after pinching. 

• Keep plants moist at all times to prevent flower buds from 

aborting. 

• Feed with 150-200ppm N to ensure vigorous growth. Maintain EC 

levels of 2.5-3.5 using the pour thru method. 

• Watch for aphids, whiteflies, mites, and sawfly larvae. 

Hostas 

Growing Hostas in Early Spring 

It is quite normal for different hosta varieties to re-emerge at 

significantly different rates in spring. Some will virtually explode 

from the soil while others are slower to emerge. The speed of 

emergence can depend on: 

• Growing Temperature: Hostas grown in a cool 40-50°F 

environment can take much longer to emerge than plants grown 

at 60-70°F. However, if you flush them out too quickly, the leaf 

substance will be thinner, so it is better to reemerge them in cool 

temperatures. 

• Length of Vernalization: Many hostas require a full 10 week 

vernalization (35°F temperatures) to grow properly the following 

spring. Hostas that do not receive the necessary cold treatment will 

take significantly longer to reemerge. Hostas received from Walters 

Gardens, Inc. in early spring will be dormant vernalized plants. 

• Cultivar/Species: Generally, tokudama and fortunei types emerge 

much slower than those with undulata, sieboldiana, plantaginea, 

and montana parentage. Long days are required for hostas to 

bulk up their foliage and root systems. 

General Recommendations for Hostas 

We strongly recommend that you pot up 

your plug and bare root hostas the summer 

prior to sale. Such hostas will develop more 

eyes, a better root system, and more mature 

traits including proper variegation. They also 

will be saleable quicker in spring and have a 

much higher perceived value. 

• Pot up plants in a well-drained, bark-based, 

soilless mix with the eyes at or just below the 

soil surface. 

• When transplanting in spring, keep 

hostas at 50°F for the first two 

weeks to promote root growth. 

Minimum temperatures may then 

be lowered to 40°F. 

• Keep soil moist early in the growing 

season without overwatering. Later in 

the season, allow soil to dry slightly 

between waterings. Dormant hostas 

require very little water. 

• Hostas will benefit from a light 

application of liquid fertilizer (20-10- 

20 with 50ppm Nitrogen) in early 

spring. Since it is critical to keep all 

granular fertilizers out of the crown 

Walters Gardens has a 

zero tolerance policy for 

Hosta Virus X (HVX), and 

tests regularly for the virus 

to avoid injury, liquid feed is safest. Alternatively, a top dressing 

of slow release fertilizer may be used. Roots will rot if too much 

fertilizer is applied. Aim for an EC rate of 1.5-2.0 using the pour 

through method. In the fall, only a light fertilizer application, if 

any, is necessary. Apply very little Nitrogen in the fall to allow 

plants to go dormant. 

• The use of a 50% shade cloth in the north (70% in the south) 

is recommended since excessive light may cause irregular 

bleached areas (sun scald) on the leaves of sensitive varieties. 

Shading will also help blue hostas retain their attractive blue 

color later into the season. 

Lagerstroemia 

• Lagerstroemia, commonly called Crapemyrtles, are traditionally 

a southern plant but because of advances in their genetics some 

varieties are now hardy to Zone 6. 30ct plugs can be planted 

in spring through summer, and will finish in 12-14 weeks in a 

premium 2 gallon container. 

• Suggested container size is 2-3 gallons. 

• Due to their southern heritage, Crapemyrtles are a heat loving 

plant and will put on the most growth in the heat of the summer. 


Culture Guide 

When planting in the greenhouse in spring, you will want to 

maintain temperatures of at least 68-70°F. 

• Crapemyrtles grow best under high light levels and in a welldrained 

media with a pH of 5.5-6. 

• They are moderate feeders, taking a constant liquid feed of 100- 

125ppm Nitrogen. 

• Crapemyrtles bloom in August on new growth and will die back 

to the ground over winter in the north. 

Lavandula (Lavender) 

Lavender is trending right now due to its multiple uses as an 

ornamental perennial, culinary herb and fantastic aromatic foliage. 

Three input sizes of lavender are available to purchase from Walters 

Gardens: 

• 30ct plugs should be planted in late winter to spring and will fill a 

trade gallon in 7-9 weeks. 

• 72ct plugs may be planted either in the late summer and sold 

the following spring, or in late winter to spring, filling a trade 

gallon container in 8-12 weeks depending on the season. 

• Bare root lavender is best planted in late winter to spring in 

1-2 gallon containers, and finishes in 8-10 weeks. The foliage 

is shaped by us, enabling you to finish an attractive plant with 

no trimming required on your part. When receiving bare root 

lavender, we recommend that it be one of the first things you 

get out of the box and plant, and water in immediately and 

thoroughly to eliminate air pockets in the media and to hydrate 

the plants. It is also beneficial to cover bare root lavender with 

remay cloth after planting to prevent the dormant evergreen 

foliage from dessication, until new roots form and can support 

the new growth. 

Most lavender requires 8-10 weeks of vernalization in order to flower, 

with the exception of SWEET ROMANCE®, which is cold beneficial 

but will flower without vernalization. All bare root lavender will have 

received the necessary cold treatment in the field. 

Lavender will perform best when planted in a well-drained mix and 

grown with moderate moisture to slightly dry. Do not grow too dry 

(do not allow to wilt) or too wet, as both extremes may lead to root 

rots. Avoid high humidity and overhead watering late in the day to 

minimize foliar issues. 

Fertilizer levels for lavender should be fairly low, in the 50-75 ppm N 

range when using constant liquid feed, as they are light feeders. 

Rhizoctonia, Phytopthora, Botrytis and other fungal pathogens 

can be problematic if grown under less than ideal conditions. A 

preventative drench after transplant and preventative sprays will 

help keep pathogens at bay. 

Lupines 

Lupines can be grown from larger 30ct plugs in spring or smaller 

72ct plugs the fall before sales. If planting in spring, grow them cool 

at 60-65°F constant temperatures. If growing in fall, keep plants 

above 50°F until they are finished and then vernalize them for 6-8 

weeks or longer in a minimally heated greenhouse or unheated cold 

frame. 

• Use a well-drained, bark based growing media with a pH of 5.8- 

6.2 to ensure proper drainage. Maintain average to moist soil 

moisture. 

• Lupines are light to moderate feeders. Fertilize with a constant 

liquid feed of 75-100ppm N at every irrigation and aim for an EC 

rate of 2.0-2.5 using the pour through method. 

• PGRs may be used to control the height of the foliage and flower 

stalks. 


Culture Guide 

Soil Level 

11/2-2” Planting Depth 

Eyes 

Peonies 

Garden Peony 

Eyes 

Crown 

Intersectional Peony 

Garden Peonies 

The most critical aspect of growing peonies is their planting depth. 

For garden peonies, the eyes on the root should be planted to a 

depth of 11/2-2 inches below the soil surface. The lower roots may 

be trimmed to fit the pot if necessary. Proper planting will help to 

ensure a good flowering performance. 

Intersectional Peonies 

For intersectional peonies, the crown should be planted 11/2-2 inches 

below soil level. If the eyes have already begun to grow, they may 

stick up above the soil a bit after planting the crown below soil level. 

General Cultural Recommendations for Peonies 

When you receive your shipment of peonies, open the boxes and 

inspect the roots. If they look dry, soak them in water for 12 hours 

or overnight before planting. If you are not able to plant them right 

away, repack them in the materials in which they were shipped and 

store them in 38-42°F temperatures for up to 10 days. 

• 2/3 eye divisions should be potted in 1 gallon containers. 

• 3/5 eye divisions should be potted in 2-3 gallon containers. 

• Use a well-drained, bark-based, commercial growing mix with a 

pH of 6.5-7.0. Peonies need good drainage and air circulation for 

disease control. 

Planting peonies in the fall will result in improved flowering the 

following spring. Fall planting is highly recommended. 

If planting peonies in the spring, it is important to grow them cool 

in order to yield stronger plants and prevent them from growing too 

fast. We recommend 45-50°F days and cold nights of 35-40°F. It 

may become necessary to run the fans in the greenhouse on sunny 

days to maintain this cool temperature. When grown at higher 

temperatures, the plants slow their bud development, the flowers 

age faster, and leaf curl may occur. 

In the spring, use a low rate fertilizer such as 18-6-8 at 100-150ppm 

at every other watering. Over-fertilization can inhibit flowering. Aim 

for an EC rate of 1.5-2.5 using the pour through method. 

Perovskia 

• Bare Root Perovskia are best planted in Spring. They should be 

potted in a 1-Gal container and kept at 68-72°F to finish in 6-8 

weeks. 

• Perovskia grown from plugs finish in a 1-Gal container as well but 

will finish in 10-12 weeks. We recommend plug Perovskia as a 

late summer planting to overwinter. 

• Vernalization is beneficial to bloom but not necessary. 

• We recommend 75-100ppm Nitrogen in a constant liquid feed but 

if you prefer slow release fertilizers we recommend a rate of 1.0- 

1.25 lbs. per cubic yard of growing media. 

• The EC rate is 1.5-2.0 using the pour through method. 

• In the landscape, Perovskia are drought tolerant. In production, 

we recommend keeping your plants moderately moist to slightly 

dry with either drip or overhead irrigation. 

• Grow this crop under clear plastic or indoors or in direct sunlight. 

Proper lighting will keep the plant more compact. 

• Perovskia overwinter best in a minimally heated greenhouse. 

They can be successfully overwintered outdoors under a frost 

blanket or in an unheated greenhouse. 

Creeping Phlox (Bare Root) 

• Since this is an evergreen perennial, it should be potted up 

immediately upon receipt. 

• Pot into wide, shallow containers such as a 7-8 inch mum pan or 

azalea pot. Standard 1-gal containers are too small for bare root 

creeping phlox. 

• Excellent root to soil contact is essential! Take care when potting 

up bare root creeping phlox to make sure all of the fine root 

mass is covered. 

• Water thoroughly after potting to allow the soil to settle around 

the roots. Then water lightly until new growth appears. 

• Creeping Phlox needs high light levels, good air circulation, cool 

temperatures (40-50°F), and an EC rate of 1.5-2.5 using the pour 

through method to thrive. 

• For spring planting, pot plants up in late March or early April (in 

the north) and place directly outside under white, lightweight, 

breathable row cover. Monitor soil moisture daily and water through 

the fabric as needed. Remove the row cover when buds appear. 

Prepare to cover the plants again in the event of a late, hard frost. 


Culture Guide 

Spigelia 

This stunning perennial is native to the Eastern United States 

and creates a splash of red in the landscape that will entice the 

neighborhood hummingbirds to stop by for a snack. They are a very 

versatile perennial, growing well in sun or part shade and in a wide 

range of soils as long as drainage is good. 

We are vegetatively propagating our spigelia to ensure good 

uniformity, and will be offering it as grade 1 bare root divisions and as 

72ct plugs. Bare root should be planted in spring to summer, and will 

take 10-12 weeks to finish depending on temperature. 72cts should be 

planted in late summer and overwintered for following spring sales. 

Spigelia does require vernalization to bloom, provide at least 8 

weeks between 35-40° F. Bare root material will have received the 

needed cold treatment in the fields. 

Higher light levels are preferable in production to produce higher 

quality plants. If toning is needed, apply Uniconazole (Sumagic/ 

Concise) starting at 5 ppm. 

Ferns 

Good irrigation practices are essential when growing ferns. Plants 

need to be kept moist, but not soaked, from the time they are potted 

up until they are planted in the ground. It is best to water early in 

the day to allow the fronds plenty of time to dry before nightfall. 

Allow the soil to dry slightly between waterings. 

Ferns can be sensitive to high salt levels incurred from fertilizing. 

Aim for an EC rate of 1.0-1.5 using the pour through method and 

use about half the amount of fertilizer you would use with other 

perennials. 

To prevent sun scorch in summer, grow ferns under at least 50% 

shade in the north and up to 70% shade in the south. 

Ferns should be planted before mid-August or wait until the 

following spring to ensure survival. Potting them up early will give 

them an adequate amount of time to become established before 

overwintering. Upon receipt of your order, it is best to place them in 

a cool, shaded location. 

Ornamental Grasses and Sedges 

• Roots must be kept moist prior to potting and plants must be 

kept from freezing, preferably above 45°F, both before and after 

transplanting. 

• Pot up in a well-drained, commercial soil mix. 

• Water sparingly until a significant amount of new growth appears. 

• Most grasses are moderate feeders and perform well with an EC 

rate of 2.0-3.0 (pour through method). Sedges are lighter feeders, 

preferring an EC rate of 1.5-2.0 (pour through method). 

Cool Season Grasses 

Cool season grasses are at their prime during the cooler months 

of fall, winter, and spring, and usually bloom before the warmer 

summer weather arrives. Many are evergreen. Cool season 

grasses should be received in fall or early spring and be potted 

up immediately. They will put on the most growth during these 

cooler months. Though they should be kept from freezing over the 

winter, they do not require much, if any, supplemental heat. Cool 

season grasses include: Calamagrostis acutiflora, Deschampsia, 

Festuca, Helictotrichon, and Sesleria. 

Warm Season Grasses 

Warm season grasses grow most actively during the warmer 

months, then flower in late summer or fall. Most go completely 

dormant in winter. Warm season grasses are not recommended 

for fall planting. It is best to receive them from early spring 

through late summer and pot them up immediately. If necessary, 

provide supplemental heat to keep the plants at 60°F or higher to 

stimulate top growth. Warm season grasses include: Andropogon, 

Bouteloua, Calamagrostis brachytricha, Hakonechloa, Miscanthus, 

Panicum, Pennisetum, Schizachyrium, and Sporobolus. 

Sedge 

Though it is not a true grass, Sedge, or Carex, tends to grow much 

like a warm season grass. It is best to receive Carex from early 

spring through late summer rather than in the fall. 

Ornamental & Edible Strawberries from Plugs 

• Plant ornamental and edible strawberries such as Fragaria a. 

‘Tristan’ in spring for summer sales. 

• Plant one 72ct plug per 1-Qt or trade 1-Gal container. 

• Grow these plants cool at 55-60°F with high light intensities for 

best results. Temperature may be raised slightly once plants are 

rooted out. Plants will generally finish in 1-Qt containers in 4-6 

weeks and in trade 1-Gal containers in 8-10 weeks. 

• Use a well-drained, balanced soil with a pH of 5.8-6.5 and an EC 

rate of 1.5-2.5 using the pour through method. 

• Maintain slightly moist soil consistently. Do not let plants dry out. 

Edible Strawberries from Bare Root 

• Plant edible strawberries such as ‘Allstar’ in spring for summer 

sales. 

• Plant one bare root per 1-Qt or trade 1-Gal container. 

• Take care when potting to spread the roots well in the container 

and to keep the crown at the soil line. Do not pot these deep. 

• Water roots in well after potting to eliminate air pockets. 

• Follow remaining guidelines for Ornamental & Edible Strawberries 

listed above. 


Culture Guide 

Tropicals 

• Recommended pot size depends on the variety. Colocasias 

typically require larger containers; plants will grow larger if given 

more root space. Smaller tropicals can be finished in 4-in to 1-gal 

containers. 

• Tropicals can be grown successfully in a general perennial soil mix. 

• Grow warm with a constant temperature in the upper 60s, 

and provide high light intensities as this will mimic their native 

environment. 

• Maintain average to high moisture levels. Do not let these plants 

dry out. 

• Once plants are actively growing, feed with 20-10-20 water 

soluble fertilizer at a rate of 75-125ppm Nitrogen at every 

watering. 

• Not all tropicals grow at the same rate. For example, Colocasias 

are very fast growers compared to Cordylines. Plan your timing 

accordingly. 

• Some tropical temperennials have very tender foliage that is 

easily torn or damaged. Take care when handling them. 

DIGIPLEXIS® 

DIGIPLEXIS® are a combination of hardy Digitalis purpurea and the 

Canary Islands native Isoplexis canariensis. These award-winning 

plants have the enviable traits of long season of flowering, heavy 

flower performance, and vigorous growth rates. 

DIGIPLEXIS® are vigorous growers and a 2-Gallon container is 

recommended. 

Plants finish in 8-10 weeks at 55-60°F. This is a tender perennial—if 

temperatures fall below 38°F there is a good chance of damaging 

the plant. 

High light levels and cool temperatures will keep them neatly 

compact. Flower color will be significantly more vibrant when grown 

in direct sunlight than under clear plastic. 

Moderate to consistent moisture levels are recommended. Drip 

irrigation is very effective at getting water past the thick foliage to 

the roots. Irrigating in the morning is more effective as this plant 

does not like to sit too wet for too long. 

DIGIPLEXIS® are moderate feeders. A constant liquid feed of 100- 

125ppm Nitrogen during the rooting stage and increased to 200- 

250ppm Nitrogen just before blooming is recommended. 

The suggested EC rate is 2.0-3.0 using the pour through method. 

Pinching the main flower stem will stimulate production of additional 

stems and bulk up the plant. If left unpinched the main flower stem 

will grow very tall and require staking. 

Succulents (Non-Hardy) 

• Finish in 1-qt containers using a coarse, very well-drained soil. 

• Be sure to wear heavy gloves when transplanting to avoid injury 

as some Agave and Mangave varieties have sharp spines. 

• Grow warm with a constant temperature in the upper 60s, 

and provide high light intensities as this will mimic their native 

environment. 

• Succulents grow best at a moderate moisture level except for 

the slow growing Agave which prefer low to average moisture. 

Hold Agave dry but give them an occasional deep watering. 

• Succulents grow well with average fertility. 

• Succulents tend to be slow growers so plan your timing 

accordingly. 

Mangave 

Mangave are a hybrid created by crossing Manfreda and Agave, 

and the result are fun plants that have the best traits of both of their 

parents. Mangave have the great habit of Agave, but are quicker 

to produce and display interesting patterns due to the manfreda 

parentage. 

Walters Gardens offers Mangave in 72ct plugs, both as single variety 

trays and in two pre-mixed trays. Plugs should be planted in quarts 

in early summer, and will take between 8-15 weeks to finish a quart 

depending on variety. Plants with broad foliage tend to be quicker 

to finish than narrow foliaged varieties. 

Mangave love warm temperatures, and should be grown under 

68-75°F + conditions. They can be held at cooler temperatures 

down to 60°F once the desired size is achieved. 

The distinctive colors and 

spotted patterns of mangave are 

intensified by UV light. During 

the winter months or when 

grown in a greenhouse under 

poly, the coloration and spotting 

will be subdued. 

A common misconception about 

mangave is that they should be 

grown dry. They actually require 

moderate moisture in order to 

achieve the best growth, but 

avoid saturated conditions as 

that can lead to crown and root 

rots – a good rule of thumb is to 

water mangave like you would a 

hosta. 

While a tray may arrive “green”, 

a few weeks under UV or sunlight 

will bring out the bright colors 


Grower’s Reference Chart 

Recommended EC Using 

the Pour Through Method 

Consistent Water Needs 

Grow Cool: 50-60° F 

Grow Warm: 65-70° F 

Start Warm: 65-70° F 

Evergreen in Some or 

All Climates 

Average Water Needs 

Long Days to Break 

Dormancy 

Recommended pH 

Low Water Needs 

Easy to Grow 

Full Shade 

Part Shade 

Full Sun 

Hardy Perennials 

Achillea 5.5-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Aconitum 5.8-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Agapanthus 6.2-6.5 1.5-2.5 ✺ ✺ ✺ ✺ 

Agastache 5.8-6.2 1.2-1.4 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Ajuga 6.0-6.5 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Alcea 5.5-6.2 2.0-3.0 ✺ ✺ ✺ 

Alchemilla 5.8-6.5 1.0-1.2 ✺ ✺ ✺ ✺ ✺ ✺ 

Allium 5.8-6.8 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Amsonia 5.6-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Anemone 5.8-6.4 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Anthemis 5.5-6.2 1.5-2.0 ✺ ✺ ✺ ✺ 

Aquilegia 5.8-6.4 1.0-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Arabis 5.5-6.5 1.0-1.5 ✺ ✺ ✺ ✺ ✺ 

Aralia 5.0-7.4 2.0-3.0 ✺ ✺ ✺ ✺ 

Armeria 5.8-6.2 1.2-1.4 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Artemisia 5.5-6.0 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Aruncus 5.5-6.5 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Asarum 5.8-6.2 1.0-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Asclepias tuberosa 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Aster 6.0-6.5 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

*For more information visit the Culture Sheets section of our website. 










All Climates 



Dormancy 



Easy to Grow 

Full Shade 

Part Shade 

Full Sun 

Astilbe 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Baptisia 5.8-6.5 2.0-3.0 ✺ ✺ ✺ ✺ 

Belamcanda 5.8-6.5 2.0-3.0 ✺ ✺ ✺ ✺ 

Bergenia 5.8-6.5 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Brunnera 5.8-6.2 2.0-2.5 ✺ ✺ ✺ ✺ ✺ 

Buddleia 5.8-6.5 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Calamintha 6.0-6.6 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Campanula 5.8-6.2 1.0-1.2 ✺ ✺ ✺ ✺ 

Cerastium 6.0-6.5 1.2-1.5 ✺ ✺ 

Ceratostigma 5.8-6.2 1.5-2.5 ✺ ✺ ✺ ✺ ✺ 

Cimicifuga 5.8-6.8 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Clematis (Bush) 5.8-6.2 2.0-3.0 ✺ ✺ ✺ 

Convallaria 5.8-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Coreopsis 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Corydalis 5.8-6.8 1.0-1.5 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Crocosmia 5.8-6.8 1.5-2.0 ✺ ✺ ✺ 

Delosperma 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Delphinium 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ 

Dianthus 5.5-5.8 1.25-2.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Dicentra 5.5-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Digitalis 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ 

Echinacea 5.5-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Echinops 5.8-6.8 1.0-1.5 ✺ ✺ ✺ ✺ ✺ 

Epimedium 5.8-6.2 1.0-1.75 ✺ ✺ ✺ ✺ ✺ ✺ 

Eryngium 5.5-6.5









All Climates 



Dormancy 



Easy to Grow 

Full Shade 

Part Shade 

Full Sun 

Geum 5.8-6.4 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Gypsophila 5.8-6.2 1.25-2.0 ✺ ✺ ✺ ✺ ✺ 

Heliopsis 5.8-6.2 2.5-3.0 ✺ ✺ ✺ ✺ ✺ 

Helleborus 5.8-6.4 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Hemerocallis 6.0-6.5 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Heuchera 5.5-6.2 2.0-3.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Heucherella 5.5-6.2 2.0-3.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Hibiscus 5.5-6.2 2.5-3.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Hosta 5.8-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Iberis 5.5-6.2 1.2-1.4 ✺ ✺ ✺ ✺ 

Iris (Japanese) 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ 

Iris (Lousiana) 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ 

Iris (Siberian) 5.0-6.8 1.0-1.5 ✺ ✺ ✺ ✺ ✺ 

Knautia 5.8-6.5 1.5-2.0 ✺ ✺ ✺ ✺ 

Kniphofia 5.5-6.0 1.5-2.0 ✺ ✺ ✺ 

Lagerstroemia 5.5-6.0 2.0-3.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Lavandula 5.8-6.2 1.25-1.75 ✺ ✺ ✺ ✺ 

Leucanthemum 5.8-6.2 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Liatris 6.5-7.0 1.5-2.0 ✺ ✺ 

Ligularia 5.8-6.2 1.5-2.5 ✺ ✺ 

Liriope 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Lobelia 5.8-6.4 1.1-1.3 ✺ ✺ ✺ ✺ 

Lupinus 5.8-6.2 2.0-2.5 ✺ ✺ ✺ ✺ ✺ 

Lychnis 5.8-6.8 1.0-1.5 ✺ ✺ ✺ ✺ 

Malva 5.2-6.5 2.0-2.5 ✺ ✺ ✺ 

Monarda 5.8-6.4 1.5-2.5 ✺ ✺ ✺ ✺ ✺ 

Mukdenia 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ 

Nepeta 6.0-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Oenothera 5.8-6.2 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Ophiopogon 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Paeonia (Garden) 6.5-7.0 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Paeonia (Intersectional) 6.5-7.0 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Papaver 5.5-6.2 1.5-2.5 ✺ ✺ ✺ 











All Climates 



Dormancy 



Easy to Grow 

Full Shade 

Part Shade 

Full Sun 

Penstemon 5.9-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Perovskia 6.0-6.5 1.2-1.4 ✺ ✺ ✺ ✺ ✺ 

Phlox paniculata 5.8-6.5 2.0-3.5 ✺ ✺ ✺ ✺ 

Phlox subulata 5.8-6.2 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Platycodon 5.5-6.0 1.5-2.0 ✺ ✺ ✺ ✺ 

Polygonatum 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ 

Primula 5.8-6.2 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Pulmonaria 5.6-6.8 2.0-2.5 ✺ ✺ ✺ ✺ ✺ 

Rudbeckia 5.8-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Salvia 5.8-6.2 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Sanguisorba 5.5-7.0 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Saponaria 6.8-7.5 1.0-1.5 ✺ ✺ ✺ 

Scabiosa 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ 

Sedum 5.8-6.5 2.0-3.5 ✺ ✺ ✺ ✺ 

Sempervivum 5.8-6.2 1.0-1.5 ✺ ✺ ✺ ✺ 

Sisyrinchium 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Spigelia 5-5=6.5 2.0-3.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Stachys 5.8-6.5 1.0-1.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Stokesia 5.8-6.8 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Tanacetum 5.8-6.8 1.5-2.0 ✺ ✺ ✺ 

Thymus 6.0-7.0 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Tiarella 5.5-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Tradescantia 6.0-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Tricyrtis 5.8-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Trollius 5.8-6.8 1.5-2.0 ✺ ✺ ✺ ✺ 

Vernonia 5.5-7.0 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Veronica 5.5-6.2 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Viola 5.8-6.8 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Yucca 6.0-6.5 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Ferns 

Athyrium 5.5-6.5 1.0-1.5 ✺ ✺ ✺ ✺ ✺ 

Dryopteris 5.5-6.5 1.0-1.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Matteuccia 5.5-6.5 1.0-1.5 ✺ ✺ ✺ ✺ ✺ 











All Climates 



Dormancy 



Easy to Grow 

Part Shade 

Full Shade 

Full Sun 

Grasses & Sedges 

Andropogon 5.8-6.3 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Bouteloua 5.5-7.0 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Calamagrostis 5.8-6.3 2.0-3.0 ✺ ✺ ✺ ✺ ✺ 

Carex 5.8-6.3 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Festuca 5.8-6.3 1.5-2.0 ✺ ✺ ✺ ✺ ✺ ✺ 

Hakonechloa 5.8-6.3 1.75-2.25 ✺ ✺ ✺ ✺ ✺ ✺ 

Helictotrichon 5.8-6.3 1.5-2.0 ✺ ✺ ✺ ✺ 

Imperata 5.8-6.3 2.0-2.5 ✺ ✺ ✺ ✺ 

Miscanthus 5.8-6.3 2.0-3.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Panicum 5.8-6.3 2.5-3.5 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Pennisetum 5.8-6.3 2.0-3.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Schizachyrium 5.8-6.3 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Sesleria 5.5-7.0 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Sporobolus 5.8-6.3 1.5-2.5 ✺ ✺ ✺ ✺ 

Fruits & Vegetables 

Asparagus 5.5-6.2 1.5-2.0 ✺ ✺ ✺ ✺ ✺ 

Rhubarb 6.0-6.5 1.5-2.0 ✺ ✺ ✺ ✺ 

Strawberries 5.8-6.5 1.5-2.5 ✺ ✺ ✺ 

Tropicals 

Colocasia 6.0-6.5 2.0-2.5 ✺ ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Cordyline 5-5-6.5 1.5-2.5 ✺ ✺ ✺ ✺ ✺ ✺ 

Digiplexis® 5.5-6.0 2.0-3.0 ✺ ✺ ✺ 

Succulents (Non-Hardy) 

Agave 6.0-6.5 0.5-1.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Hansara 6.2-6.8 0.5-1.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Manfreda 6.0-6.5 0.5-1.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 

Mangave 6.0-6.5 0.5-1.0 ✺ ✺ ✺ ✺ ✺ ✺ ✺ 



Plant Health 

Walters Gardens has made a strong commitment to provide only the 

most healthy, vigorous product to our customers. All of our crops are 

tested regularly for the most common viruses as well as additional 

genus-specific viruses where needed. Our fields and greenhouses are 

also regularly scouted for signs of pests or diseases. In addition to the 

dedicated efforts of our Growers and Plant Health Team, we make an 

effort company-wide to maintain clean and preventative practices to 

limit the spread and introduction of pests, diseases, and viruses. 

How to Identify 

Virus-Indexed Plants (VIP) 

A virus-indexed variety is one that has been tested and deemed 

free of the viruses listed (right) up to the point of testing. A bow 

tie symbol is located in the key code of each variety that has 

been virus-indexed. 

Sustainable Production Practice 

and Integrated Pest Management 

In the Fields 

Understanding the vital importance of plant health, we remain 

vigilant in preventing problems in our fields. Before a crop is planted 

in the field, we make sure our planting stock is clean and diseasefree. 

We then diversify our plantings so that disease prone items are 

never planted in the same place twice. All of the equipment used 

to plant and harvest our hosta stock blocks is sanitized between 

cultivars. We also scout weekly for weeds, insect damage, unusual 

variations in growth, trueness to type, and overall plant health. 

In the Greenhouse 

Prevention is key when it comes to pest and disease management 

in our greenhouses. We do weekly scouting for any pest, disease, or 

nutritional issues and do preventative spraying in regular intervals 

to prevent the onset of disease. Our goal is to catch problems at the 

earliest stage possible and to target the treatment to the specific 

crop before it spreads to other plants. When treatment is needed, 

we use beneficial insects or reduced-risk pesticides which target 

specific pests rather than using broad spectrum chemicals. We have 

not used neonicotinoid containing products on our production crops 

since 2014. 

Virus Prevention and Index 

We take great pride in the attentiveness of our Plant Health and 

Greenhouse staff when it comes to identifying and preventing viruses 

in our plants. All of our plants are tested on a regular basis regardless 

of appearance or history. Because there is always risk of a crop being 

exposed to a virus, and more so in a field environment, we will not 

give VIP status to a variety if we feel there is too much risk of infection 

between testing and shipping. If a variety is prone to viral infection, 

extra steps are taken to ensure that our stock and production lines 

always start with clean material. 

Plants are tested here at Walters Gardens, Inc. for the viruses listed 

below and are designated with a bow tie symbol. 

General Perennials 

• Alfalfa Mosaic Virus (AMV) 

• Alternanthera/Papaya Mosaic Virus (AltMV/PapMV) 

• Arabis Mosaic Virus (ArMV) 

• Cucumber Mosaic Virus (CMV) 

• Impatiens Necrotic Spot Virus (INSV) 

• Potyvirus Group (POTY) 

• Tobacco Mosaic Virus (TMV) 

• Tobacco Ringspot Virus (TRSV) 

• Tobacco Streak Virus (TSV) 

• Tomato Aspermy Virus (TAV) 

• Tomato Ringspot Virus (ToRSV) 

• Tomato Spotted Wilt Virus (TSWV) 

Dianthus 

• 12 General Perennial tests 

• Carnation Etched Ring Virus (CERV) 

• Carnation Latent Virus (CLV) 

• Carnation Mottle Virus (CarMV) 

• Carnation Necrotic Fleck Virus (CNFV) 

• Carnation Ringspot Virus (CRSV) 

Hosta 

• Arabis Mosaic Virus (ArMV) 

• Cucumber Mosaic Virus (CMV) 

• Hosta Virus X (HVX) 

• Impatiens Necrotic Spot Virus (INSV) 

• Tobacco Ringspot Virus (TRSV) 

• Tobacco Streak Virus (TSV) 

• Tomato Ringspot Virus (ToRSV) 

• Tomato Spotted Wilt Virus (TSWV) 

Anemone, Astilbe, Dicentra, Epimedium, Iris, Paeonia 

• 12 General Perennial tests 

• Tobacco Rattle Virus (TRV) 


Common Insects Affecting Herbaceous Perennials 

Plant Health 

Pest 

Biological Control 

Biological Control Compatible 

Insecticides 

Other Insecticides 

Aphid 

Aphidoletes aphidimyza, Aphidius 

colemani, Chrysopa carnea, 

Adalia bipunctata 

Azatin O, Botanigard, Endeavor, 

Rycar 

Altus, Horticultural oil, Orthene 

Black Vine Weevil 

Steinernema spp. and 

Heterorhabditis spp. 

Botanigard 

Orthene drench for larvae; 

Orthene or Talstar for adults 

Caterpillars 

Chrysopa carnea 

Azatin O, Botanigard, DiPel, 

Overture 

Conserve, Decathlon, 

Mainspring, Orthene 

Fungus Gnats & Shorefly Larvae 

Steinernema feltiae, Hypoaspis 

miles, Atheta coriaria 

Adept, Citation, Distance, Gnatrol 

Duraguard (SF), Talstar (FG) 

Leafhoppers Chrysopa carnea Rycar Altus, Orthene 

Leafminers Steinernema spp, Diglyphus isea Azatin O, Conserve, Citation Avid, Conserve, Orthene 

Mealybugs 

Chrysopa carnea, 

Cryptolaemus spp. 

Rycar 

Altus, Orthene Drench 

Mites 

Phytoseiulus persimillis, 

Amblyseius californicus 

Floramite, Hexygon, Ovation, 

Shuttle O, Sultan 

Avid, Judo, Pylon, Sanmite, 

Tetrasan 

Scale 

Amblyseius spp, Chrysopa 

Carnea, Cryptolaemus spp. 

N/A 

Altus, Horticultural oil, Suffoil-X, 

Orthene Drench 

Slugs & Snails N/A Sluggo Mesurol 

Thrips 

Amblyseius cucumeris, 

Amblyseius swirskii, Orius 

insidiosus, Steinernema feltiae 

Botanigard, Mainspring, Overture 

Altus, Avid, Conserve, Mesurol, 

SuffOil-X 

Whitefly 

Amblyseius swirskii, Encarsia 

formosa, Eretmocerus eremicus, 

Delphastus spp. 

Azatin O, Botanigard, Distance, 

Endeavor, Rycar 

Altus, Avid, Decathlon, Judo, 

Sanmite, SuffOil-X 

Note: Refer to product label for specific application instructions. 

Aphid Slug Leafminer damage 


Plant Health 

Common Diseases Affecting Herbaceous Perennials 

Disease 

Alternaria Leaf Spot 

Anthracnose Leaf Spot 

Aster Yellows 

Bacteria Leaf Spots (ex: 

Xanthamonas, Pseudomonas) 

Botrytis 

Cercospora Leaf Spot 

Downy Mildew 

Fusarium Crown or Root Rot 

Galls-Agrobacterium 

tumefaciens (Crown Gall) & 

Rhodococcus fascians (Leafy 

Gall) 

Favorable Environmental 

Conditions for Development 

Warm temps, humidity, 

prolonged standing water on 

leaf surface 

Warm temps, prolonged 

standing water on leaf surface 

Symptoms of infection usually 

most evident mid-spring thru 

summer 



and high humidity 

Moderate to cool temps, high 

humidity or prolonged standing 

water on leaf surface 

Moderate to cool temps and 

prolonged leaf wetness 

Warm to cool temperatures, 

prolonged standing water 

on leaf surface, high relative 

humidity, cloudy days 

Warm soil, excess water and/ 

or fertilizer 

Symptoms of infection usually 

most evident mid to end of 

summer 

Typical Symptoms Cultural Management Chemical Management 

Reddish or purple spots usually 

with brown/necrotic centers 

Tan, black, or brown leaf spots 

irregular spots; sometimes 

spores can be observed in spot 

with hand lens 

Flowers become green and 

distorted; new shoots are 

yellow, spindly, & stunted. 

Red, brown, black, purple 

irregular or round shaped spots 

with yellow halo 

White/grey spores; primarily 

attacks dead, decaying, or 

diseased plant parts and 

spreads to healthy plant tissue 

if uncontrolled. 

Spots with tan centers and 

purple borders; sometimes small 

black spores visible in center 

Faint or bright red/purple/tan 

angular leaf spots (similar to foliar 

nematodes); white fuzzy spores 

may be seen on leaf undersides 

Initially older leaves yellow & wilt; 

in time, roots & crown become 

completely brown with rot 

Crown Gall-Tumors in the shape 

of irregular spheres. Leafy Gall- 

Excessive shoot proliferation 

without elongation. 

Good air flow around plants, 

Keep foliage dry, remove 

diseased foliage 

Good air flow around plants, Keep 

foliage dry, remove diseased 

foliage 

Clean stock 

Clean stock 

Good air flow around plants to 

dry out decaying plant tissue 




Good air flow around plants; Keep 

foliage dry, decrease relative 

humidity if it's too high, remove 


Avoid overwatering, reduce 

fertilization 

Clean stock 

Affirm WDG, Broadform, Chipco 

26019, Daconil Ultrex, Heritage, 

Medallion, Pageant 

Daconil Ultrex, Heritage, 

Broadform, Pageant, Medallion, 

Cease 

Monitor for 6-spotted Aster 

leafhopper (the Aster Yellows 

vector) and start control early 

in spring. 

Camelot, Kocide, or Phyton 27 

can reduce symptoms/spread, 

but will not eliminate bacteria 

Affirm, Broadform, Chipco 

26GT, Daconil Ultrex, Decree, 

Medallion, Milstop/Cease, 

Pageant, Terraguard 

Daconil Ultrex, Eagle, Heritage, 

Protect 

Adorn, Fenstop, Micora, Orvego, 

Segovis, Segway, Stature, 

Subdue 

Chipco 26GT, Heritage, 

Medallion, Pageant, Terraguard 

None 


Aster Yellows damage on Echinacea Crown Gall Downy Mildew 

Hosta with Anthracnose 


Plant Health 

Common Diseases Affecting Herbaceous Perennials 

Disease 

Phytophthora Root/Crown Rot 

Powdery Mildew 

Pythium Root/Crown Rot 

Rhizoctonia Crown Rot 

Rhizoctonia Web Blight (Foliar 

Blight) 

Rust 

Septoria Leaf Spot 

Thielaviopsis Root/Crown Rot 

Virus 

Favorable Environmental 

Conditions for Development 

Excess soil moisture or root tips 

in standing water under pots, 

excess fertilizer, plant stress 

Moderate or cool temps, high 

humidity, cloudy days 

Excess soil moisture or root tips 

in standing water under pots, 

excess fertilizer, plant stress 

Warm temps, high humidity, 

excess water and/or fertilizer, 

plant stress 


standing water on leaf surface, 

dense canopy 

Moderate temps, prolonged 


& high humidity 

Moderate temps, prolonged 


& high humidity 

Excess soil moisture, high soil 

pH (>6.0), cool soil temps, plant 

stress 

Symptoms usually most evident 

mid-spring thru early summer, can 

persist or disappear during summer 

Typical Symptoms Cultural Management Chemical Management 

Yellow, stunted or wilted plants, 

roots turn brown, sometimes 

outer root tissue pulls away, 

leaving only vascular tube 

Powdery white/grey spots on 

leaf surface that spread to cover 

whole leaves. 

Yellow, stunted or wilted plants, 

roots turn brown, sometimes 

outer root tissue pulls away, 

leaving only vascular tube 

Foliage may turn yellow and wilt; 

reddish brown lesions/cankers on 

infected roots and crown 

Foliage becomes water-soaked and 

rots, sometimes the brown web-like 

growth if the fungus is noticeable 

Sometimes brown, red, or 

orange leaf spots on upper leaf; 

round, raised brown or orange 

pustules on the underside of leaf 

Spots have red/purple margins 

with tan, necrotic centers (can 

look similar to Alternaria) or 

brown necrotic angular spots 

Lower leaves turn yellow & wilt; 

roots start with dark brown or 

black spots & eventually turn 

completely black with rot 

Ringspots, mosaic, mottling, 

stunted growth, necrotic or 

chlorotic spots, leaf distortion 


fertilization, avoid plant stress 

Good air flow; remove diseased 

foliage 


fertilization, avoid plant stress 


fertilization 




Good air flow around plants; 


disease foliage 




Keep soil pH≤6.0, warm soil 

temps (>65 degrees); avoid 

overwatering, do not reuse pots 

or soil 

Clean stock 

Adorn, Micora, Segovis, Subdue, 

Truban 

Broadform, Eagle, Heritage, 

Milstop, Pageant, Pipron, 

Terraguard 

Segovis, Subdue, Truban 

Affirm, Broadform, Chipco 

26GT, Cleary 3336, Heritage, 

Medallion, Pageant 

Affirm, Broadform, Clearys 

3336, Daconil Ultrex, Eagle, 

Heritage, Pageant, Palladium. 

Broadform, Clearys 3336, 

Eagle, Heritage, Mural, Protect 

DF, Pageant 

Broadform, Clearys 3336, 

Daconil Ultrex, Heritage, 

Pageant 

Affirm, Banrot, Clearys 3336, 

Medallion, Terraguard 

None 


Virus in Phlox Phytophthora Root/Crown Rot 

Powdery Mildew Rust 


Summer / Early Fall Planting & 

Overwintering Recommendations 

Summer & Fall Planting 

Many experienced growers know that late 

summer and early fall are excellent times 

for planting perennials. Trials have shown 

that many varieties of perennials have a 

tremendous advantage when started the 

season prior over those planted in spring. 

They are stronger, more well-established, 

display mature characteristics, and have 

a higher perceived value. The pictures on 

the next page show a few key genera that 

benefit greatly from late summer planting. 

A trial conducted at Walters Gardens 

comparing the finish rates of freshly dug, 

actively growing hostas to those of freshly 

dug, dormant hostas grown in summer 

demonstrated that those finished from 

dormant plants are far superior in size, bulk, 

and root mass than those finished from 

actively growing plants. 

On p. 39 you’ll find a chart listing some 

types of perennials that benefit greatly 

from summer and early fall planting. 

Perennials such as Hosta and Hibiscus 

require long days and some heat to grow, 

so they need to be planted in summer 

rather than fall when the light intensities 

are greater and temperatures are warmer. 

Note on this chart the color coding which 

indicates whether the plants should ideally 

be overwintered indoors or out. 

Planting Bare Root Hostas in Summer 

As a result of the trial, bare root hostas 

are now dug from our fields in early 

spring before they break dormancy and 

held in freezers until they are shipped to 

our customers from early June into early 

August. We recommend that our customers 

receive their bare root hostas as early in 

summer as possible to take advantage of 

the long, warm growing days, resulting in a 

higher quality finished crop. 

Overwintering 

Precaution 

If properly cared for going into 

winter, perennials that are potted 

up in summer and early fall should 

overwinter well and emerge as large, 

vigorous plants in spring. Overwintering 

methods are described in the section 

below. If you do not have the necessary 

facilities for overwintering your 

perennials, we suggest that you have 

your order shipped in spring rather than 

in summer or fall. 

Factors such as soil moisture, 

temperature fluctuations, and root 

development in the container can 

greatly affect a plant’s survival. Since 

there are so many factors beyond our 

control, Walters Gardens, Inc. does 

not guarantee the survival of plants 

overwintered in containers or in the 

ground. 


Benefits of Summer and Early Fall Planting 

You’ll save money. 

When you grow perennials in summer and fall, there is no need for costly supplemental 

heating or lighting. There’s less maintenance cost too since perennials 

grown outdoors tend to grow more compactly because the wind, rain, and sun act 

as natural PGRs. 

You’ll save time and labor. 

If you have overwintering capabilities, it is not necessary or even recommended to 

plant all of your plants in spring. You’ll be better off if you time your crops properly, 

splitting them into two groups: those best planted in summer or early fall (see chart 

below for some examples) and those that are best planted in spring. This will save 

time and make better use of your labor force–and of course lighten your stress 

load–in the spring. 

You’ll have larger, better performing 

plants to sell in spring. 

It’s no doubt that some perennials perform exponentially better if potted in summer 

or early fall the year before they are sold. The perennials pictured here are great 

examples of that. 

Perennials build stronger root systems, have larger crowns that flush out nicer, 

and are more floriferous the following spring when they are planted summer or fall 

before. They’ll not only have a higher perceived value–they will deliver a stronger 

performance for everyone from the grower to the consumer. 

Overwintering Methods 

If properly cared for going into winter, perennials that are potted up in summer and 

early fall should overwinter well and emerge as large, vigorous plants in spring. 

There are four basic methods of overwintering perennials: Thermoblanket Technique 

• Sandwich Method • Minimally Heated Greenhouse or Polyhouse • Unheated Polyhouse 

Under a Foam Blanket. Details on the following pages. 

If you do not have the necessary facilities for overwintering your perennials, we 

suggest that you have your order shipped in spring rather than summer or fall. 

Left: Vernalized 20ct Hosta planted in a Premium 1-gal pot in spring. 

Right: Fresh 20ct Hosta planted in a Premium 1-gal pot in late summer. 

Hostas planted earlier develop more eyes, a better root system, and 

more mature traits including proper variegation. 

Left: Vernalized 20ct Monarda planted in a trade 1-gal pot in spring. 

Right: Fresh 72ct Monarda planted in a Premium 1-gal pot in late 

summer. The smaller plug filled out the larger container with fuller 

foliage and more flowers, commanding a higher price at retail. 

Summer Planting 

Aruncus 72ct Grasses - Sedges Monarda 72ct 

Brunnera 72ct Grasses - Warm season Perovskia 72ct 

Coreopsis - Threadleaf 72ct Gypsophila 72ct Phlox - All 

Daylilies - Any Size Heliopsis 72ct Rudbeckia ‘Little Goldstar’ 72ct 

Dianthus 72ct Hostas Sedum - Upright forms 72ct 

Dicentra 72ct Leucanthemum 72ct Stokesia 72ct 

Euphorbia 72ct Ligularia 72ct Veronica 72ct 

Geranium 

Ligularia ‘Bottle Rocket’ benefits greatly from being planted the year 

before it is sold. Those potted in late summer for sales the following 

spring (right) are much fuller with larger leaves and more flowers per 

plant than those potted up and sold the same spring (left). 

Aquilegia 72ct 

Epimedium 20ct 

Grasses - Cool season 

Paeonia - Garden and 

Intersectional types 

Early Fall Planting 

Color Key: 

Primula 72ct 

Pulmonaria 72ct 

Salvia 72ct 

Tiarella 72ct 

Best Overwintered Outdoors 

Best Overwintered Indoors 



Going into Winter 

Rooting 

The most important factor in overwintering perennials is having 

healthy, well-rooted plants going into winter. Poorly rooted and potbound 

plants tend to overwinter poorly. Time the delivery of your 

bare root and plug perennials so that they can be well-rooted in 

their containers by the time winter arrives. 

Shearing and Moisture 

• Evergreen Perennials 

Perennials with evergreen foliage should not be cut back going 

into winter. In order to prevent crushing or rotting the foliage, 

they are best stored either on their sides or with an inverted tray 

placed atop their foliage. 

• Dormant Perennials 

Most leafy perennials with dormant foliage will benefit from 

being cut back and cleaned up before winter. Trim their foliage 

back to the crown before storing them for winter. 

• Moisture 

When preparing your plants to be overwintered, check their roots 

to make sure they are not dry. Most perennials like to have moist 

roots going into winter since the moisture helps to insulate the 

roots and prevent dessication. However, there are exceptions of 

plants that prefer to be stored dry. 

Baiting for Rodents 

Several blends of rodent bait are available. Rotating the types 

of baits used will increase their effectiveness. Begin baiting for 

rodents about a month before covering your plants. This will help 

to reduce their population going into winter. Place traps every 

15-20 feet. Be sure to use pet-friendly traps to prevent accidentally 

poisoning your pets. 

Deciding When to Cover Your Plants 

Timing is critical when it comes to covering your plants for winter. 

If covered too early, heat can build up under the cover and damage 

the plants. If the cover is left on too long in spring, the plants can 

put on a soft flush of new growth that is easily damaged by late 

frosts. When deciding when to cover your plants for winter, be sure 

to monitor weather conditions closely. Nighttime temperatures near 

freezing allow the plants to harden off before covering, but if the 

forecast predicts nighttime temperatures below 25°F, it’s time to 

cover your plants. 

Dealing with Extremes 

Extreme Cold 

When perennials are overwintered above ground in containers, 

they are effected to a greater degree by extreme winter 

temperatures. Wide fluctuations between day and nighttime 

temperatures, particularly in late winter and early spring, can 

cause the plants to freeze and thaw, potentially damaging the 

plants. Therefore, containerized perennials must be protected from 

extreme cold when they are overwintered. They should be stored at 

temperatures above freezing. 

Excess Heat 

On sunny days in late winter and early spring, heat can rapidly build 

up in polyhouses. Good air circulation and ventilation is critical to 

preventing plants from growing prematurely. Plants stored outside 

on these sunny days may need to be uncovered and then recovered 

based on the weather patterns. 

A well-developed, 

healthy root 

system will solve a 

number of common 

overwintering issues 



Overwintering Challenging Plants 

Many kinds of perennials overwinter easily. However, some require 

a little special treatment to make it through the winter in containers 

successfully. Here are some tips for those types of plants. 

Perennials that like to be kept dry 

• Perennials that like to be kept dry during the winter should be 

planted in a very well-drained growing media that can stay 

relatively dry over the winter. 

• Be sure to protect these types of plants from heavy fall rains 

and from below freezing temperatures while they are being 

stored for winter. 

• Trim their foliage back and lay the pots on their sides if possible. 

Make sure that no covering material comes in direct contact 

with the foliage. 

Ornamental Grasses 

• Before potted grasses are stored for winter, water them 

thoroughly. After they have gone dormant, they will need little 

to no water until the temperatures begin to warm up again 

the following spring. At that time, watering can be resumed as 

needed to maintain proper moisture levels. 

• After the plants have gone completely dormant for the winter, 

you can trim the foliage all the way back. Do not cut the foliage 

back until it is totally dormant. 

• When overwintering grasses, make sure the temperature of the 

root ball remains at or above freezing. Exposure to temperatures 

below freezing may result in plant losses. 

• Be sure to bait liberally for rodents since they have a fondness 

for grasses. 

Outdoor Overwintering Methods 

Thermoblanket Technique 

An insulated foam blanket (polyfoam or microfoam) is placed over the containers during the coldest months of the year. It is important 

that the blanket be covered by white reflective nursery polyfilm, preferably 4-mil one year white poly. Pull the plastic tight over the 

containers and secure the edges about 12 inches beyond the pots with concrete blocks. 

Sandwich Method 

Plastic sheeting or spun-bonded fabric is placed directly over the plants and then covered with a 12 inch deep layer of straw. The 

straw layer is then covered with another layer of plastic sheeting. This technique is especially effective in northern regions where 

temperatures remain consistently cold all winter long. 

Frost Blanket Method (for hardy plants in zones 5 or warmer) 

In this method, pots are set directly on the ground and covered with a heavy frost blanket once the temperatures dip below 25°F. 

Pull the blanket tight over the containers and secure the edges about 12 inches beyond the pots with stakes or blocks. This method is 

best used in northern climates where temperatures remain consistently cold all winter. Snow cover is beneficial, but not required for 

overwintering success. 

Indoor Overwintering Methods 

Greenhouse or Polyhouse Kept at Low Temperatures 

This overwintering method is the best for temperature control, especially if minimal heat is used. It also gives you more control over 

moisture levels, growth, and heat build-up. Good air circulation and ventilation is critical with this method. Pubescent plants such as 

Stachys are best overwintered in a polyhouse kept at low temperatures since these kinds of plants resent being covered with foam. 

Unheated Polyhouse Under a Foam Blanket 

With this method, the containers are stored in a narrow hoop house which is covered with white poly. Foam blankets are placed over the 

plants. The house is not heated, so it is possible for plants to freeze using this method. 


Overwintering Methods 

Echinacea 

• Echinacea tends to overwinter better in larger containers, so we 

recommend that you pot them up into 1-gal containers by early 

fall at the latest. It is best to root them in completely before they 

go naturally dormant. 

• When receiving Echinacea in summer, we recommend that 

you do one preventative fungicide drench immediately after 

transplanting, and another drench about 14 days later. This 

can help to protect the plants from disease as they begin to go 

dormant in fall. 

• Before overwintering, it is best to trim the plants back lightly 

and allow what remains to go fully dormant, removing the dead 

foliage in spring. Removing the foliage all the way to the crown 

before overwintering encourages botrytis to set in, so take care 

not to trim plants too far back (no more than halfway). 

• When overwintering finished Echinaceas, hold plants at a 

constant temperature of 38-40°F. 

• Keep plants on the dry side, but not too dry or it may be difficult 

to rehydrate them if they’ve dried out too much. 

• Monitor salt levels and keep soluble salts low. 

Hostas 

Best Method - Overwintering in Unheated Structures Covered with 

White Copolymer 

• Place the pots inside the unheated structure and cover them 

with microfoam. Turn larger pots on their sides if necessary. 

• Bait liberally for mice. 

• As the warmer days of spring arrive, remove the microfoam 

cover. 

• Once the volatile spring weather has subsided, take the white 

copolymer off the structure and replace with 50% shade cloth (or 

70% for blue hostas). 

• If necessary, open the ends of the houses to provide ventilation. 

Good Method - Overwintering in Minimally Heated Polyhouses 

• Place the plants inside the minimally heated polyhouse and do 

not cover them. 


• Maintain temperatures above freezing. 35°F works well. 

• Once the volatile spring weather has subsided and 

temperatures have moderated, the plants may be moved 

outside for finishing off. 

• Be sure to provide at least 50% shade in the north and 80% 

shade in the south. 

Not Preferred - Overwintering in Cold Frames 

• This overwintering method is not preferred because the plants 

become exposed to extreme temperature changes along with 

excessive wind and moisture once the covering is removed in 

spring. This can cause foliage and root damage, possibly leading 

to plant losses. 

• If you must overwinter your hostas in a cold frame, turn the 

larger pots on their sides if possible. 

• Cover the pots with a layer of microfoam and a layer of white 

copolymer. Remove this covering in early spring. 


Peonies 

It is best to overwinter potted peonies in a covered structure such as 

a greenhouse or covered polyhouse. 

Peonies require 500-700 hours at 32-37°F to be vernalized. 

After that, it is best to let them acclimate naturally to outdoor 

temperatures. 

Please note: Peonies received after January 1 have already been 

vernalized at Walters Gardens. 

Tender Perennials 

• Tender perennials should be treated as annuals and kept actively 

growing in a warm area (minimum 55°F) through the winter 

months. 

• Succulents require very little water during the winter. 

• Tropical Perennials prefer slightly moist soil. 


Additional Resources 

Growing perennials is what we do, and we’ve been doing it for over 70 years. We are here to help our customers be more successful growers 

so they can grow their businesses too. Our knowledgeable staff is always ready to help you find the answers to your questions, whether 

you’re brand new to the industry or one of our many longtime loyal customers. In addition to the information provided in this Simple, Sensible, 

Solutions® guide, here are some more recommended resources. 

Recommended Websites 

• Walters Gardens: www.WaltersGardens.com 

• Proven Winners professional growers site: www.PWCertified.com 

• Michigan State University Extension Floriculture Team — 

Herbaceous Perennial Plant Production: 

http://www.flor.hrt.msu.edu/perennials/ 

• Cornell University Cooperative Extension — 2012 Pest 

Management Guide for the Production and Maintenance of 

Herbaceous Perennials: 

http://ipmguidelines.org/HerbaceousPerennials/ 

• University of Vermont Extension — Perry’s Perennial Pages: 

http://www.uvm.edu/~pass/perry/ 

Recommended Books 

Perennial Solutions—A Grower’s Guide to Perennial Production 

Author: Paul Pilon 

Respected Green Industry consultant 

Paul Pilon has compiled a comprehensive 

book covering all aspects of producing 

perennial crops--propagation, fertility, 

media, pest and disease management, 

weed control, height control, and 

overwintering. A large section of the 

book is devoted to forcing perennials into 

bloom to maximize sell through at the 

retail level. 

Visit www.PerennialSolutions.com for helpful articles and 

additional information from Paul Pilon. 

Ball Redbook—Volume 2: Crop Production 18th edition 

Editor: Jim Nau 

Offers professional tips on greenhouse 

horticulture, from pest control to 

plant nutrition. 162 flower, herb, and 

vegetable crops are covered. An essential 

resource for growers that offers advice 

and techniques that work in real-life 

production. 

Trade Magazines 

• GrowerTalks 

• Green Profit 

• Greenhouse Product News (GPN) 

• Greenhouse Grower 

• Garden Center Magazine 

• Greenhouse Management 

• Nursery Management 

• Greenhouse Canada 

Consults from Walters Gardens 

We’re growers just like you and we’re here to help. If you need help 

with something that is not covered here or have other growing 

questions and concerns, please feel free to contact Walters 

Gardens and we will do our best to help you resolve the issue. We 

are happy to do whatever we can to help you be successful with 

our bare root and plug perennials. 

Pictured here are Laura Robles, Barb Balgoyen, and Janet DeVries. 

Laura is our Trial Manager with many years of experience growing 

finished product for trials, events, and retail. Barb and Janet both 

have years of experience answering technical questions. 

Laura Robles 

Trial Manager 

lsr@waltersgardens.com 

Barb Balgoyen 

Technical Customer Care Rep 

1-800-925-8377 ext. 1202 

blb@waltersgardens.com 

Janet DeVries 

Technical Customer Care Rep 

1-800-925-8377 ext. 1206 

jld@waltersgardens.com 

Culture Sheets 

Cultural sheets for most of the perennials we offer can be found 

on www.WaltersGardens.com. They contain detailed information 

such as growing temperatures, soil pH, planting level, weeks to 

finish, watering, fertilizing, and pest and disease management 

recommendations. 


Walters Gardens 

Home of Proven Winners® Perennials 

P.O. Box 137 • Zeeland, MI 49464 • Phone: 888-925-8377 • Fax: 800-752-1879 • Email: sales@waltersgardens.com 

www.WaltersGardens.com • www.PerennialResource.com • www.ProvenWinners.com 

Copyright © 2019 Walters Gardens, Inc. No portion of this booklet may be reproduced without permission from Walters Gardens, Inc.

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