Site Considerations for Vineyards in Iowa - Viticulture Iowa State ...

Site Considerations
for Vineyards in Iowa
Dr. Paul Domoto
Dept. of Horticulture
Iowa State University

Site Considerations
Climate
• Winter
Temperatures
• Spring Frosts
• Length of Growing
Season
• Growing Degree
Days
• Precipitation
Topography
• Elevation
• Degree of
Slope
• Direction of
Slope
Soils
• Drainage
• Moisture Holding
Capacity
•pH
• Fertility
• Organic Matter

Winter injury of the primary cane bud.

Temperature
Macroclimate
(Large Area)
• Latitude
• Nearness to large
bodies of water *
• Elevation *
* Not factors in Iowa.
Mesoclimate
(Local Area)
• Topography
Elevation
Degree of slope
Direction of slope
• Bodies of water
• Nearness to cities

Classification of Vine Hardiness
Temp.
(F o )
> 0
-5
Based on Temperature
at Which Injury Begins to Occur
Category
V. cold
tender
Cold tender
Suitable Type
Almost any.
Most northern vinifera.
-10
-15
< -20
Moderately
Hardy
Hardy
Very hardy
Hardy vinifera, moderately
hardy French hybrids.
Hardy French hybrids, most
labrusca.
Hardy labrusca, most riparia
hybrids.

Current USDA Zone Hardiness Map
Due to elevation of the recording sites in respect
to the topography of the surrounding area.

By James D Giglierano; adapted from Iowa Geology 1999, Iowa DNR

Avoid obstructions
On calm, clear nights
cold air settles
To avoid spring frosts and extreme winter freezes,
plant at least 50 feet above the valley floor.
From ISU Ext. Pm-672b

50-Yr Avg. Min. Temperature
City
City influence
Elevation
Northern boundary of “5a” is risky because injury can
occur when vines are not at their maximum hardiness.

Grape Hardiness Curve
30
20
10
Temperature F
0
-10
-20
-30
-40
Bark
Wood
Fruit Bud
-50
5-Sep 5-Oct 5-Nov 5-Dec 5-Jan 5-Feb 5-Mar 5-Apr 5-May

Old USDA Zone Hardiness Map
4b
5a
5b
Old map safer for “4b”; 50-yr map safer for “5b”.
Best to plant “Hardy” and “Very Hardy” varieties.
From ISU Ext. Pm-453

Length of the Growing Season
Frost-Free
Free
Days
< 150
150 to 160
160 to 170
170 to 180
> 180
Suitability for Grapes
Unacceptable
Marginal: Only early season
maturing varieties.
Satisfactory: Early & most
mid-season maturing varieties.
Good: Early, mid-season &
some late-season varieties.
Excellent: Most varieties.

Frost Free Days

Grape Growing Regions
based on Growing Degree Days (Winkler)
Region
I
II
III
IV
Degree
Days
< 2,500
2,501 to
3,000
3,001 to
3,500
3,501 to
4,000
Suggested Varieties
Early ripening varieties to
achieve high quality.
Early and mid-season table
varieties.
High production of standard
to good quality table wines.
High production, but table
wine quality will be
acceptable at best.

Growing Degree Days

Average Annual Precipitation

Direction of the Slope
can influence growing conditions
N
W
E
S

Exposure to Sunlight
N
Lowest
W
Intermediate
-*
S
Greatest
E
Intermediate
+
* Under moisture stress conditions stomates
close in the afternoon, and photosynthesis stops.

Accumulation of Heat Units
N
Lowest
W
Intermediate
+*
S
Greatest
E
Intermediate
-
* Warmer in the afternoon

Risk of Spring Frosts
(Warming up in the Spring)
N
Lowest
W
Intermediate
+
E
Intermediate
-
S
Greatest

Plant’s Water Requirement
N
Lowest
W
Intermediate
+
E
Intermediate
-
S
Greatest

Risk of Fluctuating Winter
Temperatures
N
Lowest
W
Intermediate
+
E
Intermediate
-
S
Greatest

Iowa Soils
Glacial origin

21 Soil Associations

Soil Selection Factors
• Internal Drainage Characteristic
Most important
Roots need aeration to function
• Moisture Holding Capacity
Texture
Depth
•pH
• Fertility

Soil Information is Available in
County Soil Survey
• Soil Series Description:
Texture, Drainage, Fertility, Erosion
• Soil Profile Classification:
Structure
• Table of Engineering Index Properties:
Soil texture classification by depth
• Table of Physical & Chemical Properties:
Permeability, Available water holding
capacity, Organic matter content

Soil Drainage Classification
Very poorly drained
Poorly drained
Somewhat poorly drained
Moderately well-drained
Well-drained
Excessively drained
AVOID
Avoid
Marginal
Suitable
Ideal
Marginal

Reasons for Poor Soil Drainage
• Poor surface runoff
Slope
Depressions
• Sub-surface
seepage
•Texture
High clay content
• Impervious layer in
substrata
Clay layer
Compacted layer
Abrupt textural
change
• High water table

Moisture Holding Capacity
Soil Texture
Soil Depth

Available Soil Moisture
Texture
Sand
Loamy sand
Sandy loam
Loam
Silt loam
Clay loam
Clay
Inches
Per foot
0.5
1.0
1.5
2.0
2.5
2.5
2.0

Soil M oisture T ension (- Bar)
16
14
12
10
8
6
4
Available Soil Moisture
Sand
Silt
Clay
2
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Percent Soil Moisture

Soil Texture
• Too high a percentage of clay is
undesirable because of the lack of
aeration.
• Too high a percentage of sand is
undesirable because of the lack of
moisture holding capacity. The
exception is when irrigation is practiced.

Soil Depth
Available Soil Moisture @ 80% Depletion
Texture
1 foot
2 feet
3 feet
Sand
Loamy sand
Sandy loam
Loam
Silt loam
Clay loam
Clay
0.4
0.8
1.2
1.6
2.0
2.0
1.6
0.8
1.6
2.4
3.2
4.0
4.0
3.2
1.2
2.4
3.6
4.8
6.0
6.0
4.8

Soil pH for Grapes
• Optimum:
American: 5.0 to 6.5
French Hybrid: 5.5 to 6.5
Will do well up to pH of 7.0
• Iowa Soils:
4.5 for some sands in eastern Iowa
8.4 in northwest Iowa
• Adjust Soil pH:
Below 5.5 - bring up to 6.5 with lime.
Above 7.0 – consider lowering to 6.5
with sulfur, or using acid forming
fertilizers (ammonium sulfate).

Soil Fertility
• Least concern when selecting a site.
Can amend the soil.
• Iowa Soils:
Concern for K, Zn, & maybe P.
• Pre-plant Soil Tests:
Test: pH, P, K, Zn, & organic matter content.
Ca (in lime), P, & K move very slowly in the soil &
are very difficult to correct after planting.
• Collect samples from 2 depths:
0 to 6 (8) inches - Past fertilizer history
6 (8) to 12 (18) inches - Parent material

Soil Organic Matter
• Improves soil structure, moisture
retention and fertility. (2 to 3%)
• Iowa Soils:
Range from < 1% up to 20%
Well-drained soils in the 3 to 4% range
OM is higher in poorer drained soils.
• Grapes grown on high organic soils tend
to be less winter hardy.
Release of N from organic matter.
Indeterminate growth habit of grapes.
Cold acclimation.

Darker the color, higher the organic matter content.

Summary of Site Considerations
• Select an elevated site to avoid spring frost &
extremely low winter temperatures.
• Select a deep, well-drained soil that has an
adequate moisture holding capacity, and does not
contain excessive organic matter. Check your
County Soil Survey.
• Test the soil before planting for pH, P, K, Zn &
organic matter content. Amend the soil as needed.
• Select and plant grape varieties that are adapted to
your site regarding winter temperature tolerance,
length of growing season, and accumulated
growing degree days.