Root-Damaging Temperatures, Vol. 12, Issue 5

ORNAMENTALSNORTHWESTARCHIVESSept.–Oct. 1988Vol. 12, Issue 5Pages 9-14J.L.Green, OSUROOT-DAMAGING TEMPERATURES-The actual killing temperature will vary with the degree of plant dormancy at the time ofexposure to the low temperature. When plants are preconditioned for lowtemperature storage andthe temperature remains uniformly low prior to exposure to cold-temperature, the roots willgenerally survive provided that the temperature does not go below the average killingtemperature for the species.However, if the low-temperature follows a period of fluctuating temperatures, especiallytemperatures that are conducive to growth, the roots could be injured at temperaturessignificantly higher than the average killing temperature. Also, the roots of newly rooted cuttingshave a tendency to be less tolerant of cold-temperature stress than plants with a year or more ofgrowth."To minimize root injury, plants should be storedat a temperature at least 3-5°F above the averageroot- killing temperature." - Harold Davidson andRoy Mecklenburg.1981. Nursery Management -Administration And Culture. 450 pages. Prentice-Hall, Inc.In the following table, non-notated temperatures were reported by Bruce Briggs (1980Ornamentals Northwest Seminars - based on observations at the Briggs Nursery in Olympia,WA) and data reported by John R. Havis (1976, HortScience 11(4):385-386), and Peter L.teponkus, George L. Good, and Steven C. Wiest (1976, American Nurseryman 144(6):16, 76-79).

G = Reported by Francis R. Gouin, American Nurseryman,October 1, 1977, pp 56-57. These are thetemperatures that will injure immature and possibly matureroots, but will not result in 100 percent kill of theroot systems in moist soils.DECIDUOUS PLANTSGenus species ................................................... °_FAcer circinatum, Vine Maple ................................. 0Acer ginnala, Amur Maple .................................... 0Acer macrophyllum, Bigleaf Maple ......................... 0Acer negundo'Variegatum',Variegated Box Elder ........................................ 10Acer palmatum, Japanese Maple ........................... 15'Atropurpureum ............................................ 15 (G)Acer platanoides, Norway Maple ............................ 0Acer rubrum, Red Maple ....................................... 0Acer saccharum, Sugar Maple ................................ 0Aesculus hippocastnum,Common Horsechestnut ....................................... 0Berberis thunbergii,Japanese Barberry .......................................... 10-15Betula papyrifera, Paper birch .............................. 0Betula pendula, European White Birch ................ 0Betula pendula 'Darlecarlica' ('Laciniata'),Cutleaf Weeping Birch ......................................... 0Carpinus betulus fastigiata, NarrowEuropean Hornbeam ............................................ 0Catalpa speciosa, Western Catalpa ....................... 0Chaenomeles speciosa, Flowering Quince……… 5Cornus floridaEastern Dogwood ............................... …..20 22 (G)Cornus mas, Cornelian Cherry ...........................18Cornus nuttallii, Pacific Dogwood .....................22Corpus stolonifera, Red Osier Dogwood ……... 18Cotinus coggygria, Smoketree ............................18Cotoneaster adpressus praecox .....................12 (G)Cotoneaster congestus ................................... 25 (G)Cotoneaster dammed ................................. 23 (G)'Skogholmen…… ...................................... 20 (G)Cotoneaster horizontalisRock Cotoneaster ......................................17 (G)Deutzia gracilis, Slender Deutzia ........................15Fagus sylvatica `Purpurea', Purple Beech……... 15Ginkgo biloba, Ginkgo, Maidenhair Tree ..……. 15Gleditsia triacanthos `Sunburst'Sunburst Honey Locust ................................... 10Koelreuteria paniculataGoldenrain-tree ...........................................16(G)Liquidambar styracifluaAmerican Sweetgum ....................................... 15Liqustrum vulgareCommon or English Privet ................................5Liriodendron tulipifera Tulip Tree .................. 18Magnolia x 'Ricki' ........................................... 20Magnolia x SoulangeanaSaucer Magnolia .......................................23 (G)Magnolia stellata, Star Magnolia ..........17 22 (G)

Oxydendrum arboreum, Sourwood ................. 10Philadelphus cultivarsMock Orange cultivars .................................... 15Potentilla fruticosaPontentilla Cinquefoil ................................. -9 (G)Prunus blireana (blireiana)Blireana Flowering Plum ................................. 10Prunus serrulata 'Shirotae'Mt. Fuji Flowering Cherry ............................. 10RhododendronDeciduous Azalea ................................................12Exbury hybrid .............................................. 17 (G)R. prunifolium ...............................................20 (G)R. schlippenbachi ......................................... 15 (G)Rhus typhina, Staghorn Sumac ............................0Stephanandra incisa ....................................... 18 (G)EVERGREEN PLANTSAbelia grandiflora, Glossy Abelia ........................18Abies amabilis, Silver Fir .........................................0Abies concolor, White Fir .....................................0Abies grandis, Grand Fir .......................................5Abies lasiocarpa, Alpine Fir ...................................0Abies procera, Noble Fir .......................................0Arbutus menziesii, Madrona ...............................20Arbutus unedo, Strawberry Tree .........................20Aucuba japonicaAucuba, Japanese Aucuba ............................... 24Berberis julianae, Wintergreen Barberry …...... 15Berberis verruculosa, Warty Barberry ............... 5Buxus sempervirensEnglish Boxwood ...............................……15, 27 (G)Calluna vulgaris, Scotch Heather ........................ 15Calocedrus decurrens, Incense Cedar .................. 0Camellia japonicaCommon Camellia varieties .............................24Camellia sasanquaSasanqua Camellia varieties .............................24Cedrus atlantica 'Glauca'Blue Atlas Cedar .............................................10Cedrus deodara, Deodar Cedar .......................10Chamaecyparis lawsoniana 'Allumii'Allumi Cypress, Blue Lawson Cypress .......... 12'Ellwoodii', Ellwood Cypress .......................... 12Chamaecyparis obtusa, Hinoki Cypress ............0Chamaecyparis pisifera 'Filifera'Thread Cypress, Threadbranch Cypress ………...0Choisya ternata, Mexican Orange ...................20Cistus corbariensis, White Rockrose ...............20Cortaderia selloana, Pampas Grass ...................24Cryptomeria japonica ....................................17 (G)'Elegans' .............................................................. 15Cytisus praecox .............................................16 (G)Moonlight Broom ............................................... 12

Daphne cneorum ..........................................23 (G)Rock Daphne, Garland Daphne ..........................18Daphne odora, Winter Daphne ...........................22Erica carnea, Heath .............................................18Escallonia rubra, Escallonia ...............................18Euonymus alata ............................................19 (G)Euonymus fortunei'Argenteo-marginatus' ..................................15 (G)'Carrieri' .........................................................15 (G)'Colorata' .........................................................5 (G)'vegetus' .........................................................23 (G)Euonymus kiautschovicus (patens) ...........22 (G)Fatsia japonica, Fatsia, Aralia ............................. 22Gaultheria shallon, Salal ..................................... 12Hedera helix 'Baltica' ..................................... 15 (G)Hypericum species ........................................ 23 (G)Ilex aquifolium, English Holly ............................20Ilex 'Blue Holly' ................................................ 5Ilex X meserveae (I. aquifolium x I. rugosa)Ilex cornuta 'Burfordii'Burford Holly .....................................................20'Dazzler' .........................................................25 (G)'Nellie Stevens' ..............................................23 (G)Ilex crenata 'Convexa' ............................... 18 23 (G)'Helleri', 'Hetzi' ..............................................23 (G)'Stokes'............................................................23 (G)Ilex glabra .................................................16 (G)Ilex meserveae ...........................................23 (G)Ilex opaca .................................................23 (G)Ilex hybrid, `San Jose' ...............................22 (G)(I. X altaclarense 'Wilsonii' & I. sikkimensis)Juniperus chinensis 'Kaizuka' (`Torulosa'). 20`Old Gold' ...........................................................5'Pfitzerana', Pfitzer Juniper .................................0Juniperus conferta, Shore Juniper ............. 12 (G)Juniperus horizontalis 'Douglasi' .................... 0 (G)'Plumosa' ....................................................... 12 (G)Juniperus squamata ...................................12 (G)Kalmia latifoliaKalmia, Mountain Laurel ...................... 0 15 (G)Leucothoe fontanesiana (catesbaei)Drooping Leucothoe ...................................5 (G)Ligustrum japonicumWaxleaf Privet, Japanese Privet ........................ 20Magnolia grandiflora, Southern Magnolia…. 20Mahonia aquifolium ...................................... 10 (G)Oregon Grape ......................................................15Mahonia bealei ......................................... 23 (G)Mahonia nervosaLow Oregon Grape, Cascades Mahonia ….15Nandina domesticaNandina, Heavenly Bamboo ...........................20Osmanthus delavayiDelavay Osmanthus .........................................24Osmanthus heterophyllusHollyleaf Osmanthus ....................................... 20Pachysandra terminalis …………………….15 (G)Pernettya mucronata, Chilean Pernettya …... 18Photinia fraseria, Fraser Photinia …………….12

Vaccinium ovatum, Evergreen Huckleberry,Box Blueberry .................................................15Viburnum burkwoodiiBurkwood Viburnum .....................................18Viburnum carlesi …………………………15(G)Viburnum davidii, Davidi Viburnum ……….18Viburnum plicatum 'tomentosum' ………20 (G)Vinca minor ……………………………..15 (G)Yucca filamentosaAdam's Needle Yucca …………….…15