DAVIDSON, HAROLD. 1985. Woody plants can survive with good overwintering practices. Am. Nurseryman 161(6): 91-95, 98, 100-101.
Periodically, winter can have disastrous effects on plants that are normally considered hardy. Late winter (March and April) is a good time to assess damage, evaluate its cause or causes, and make plans to prevent or minimize future damage. For practical purposes, winter injury to woody plants can be classified under six categories: freeze injury, frost crack, desiccation, breakage, heaving, and girdling injury. Freeze injury occurs most frequently when non-indigenous species are grown in areas where winter temperatures drop below their individual freezing points. Frost crack causes a tree trunk to split vertically. Generally, the crack appears on the tree’s southwest side. Desiccation, or drying out of foliage, is a form of winter injury most commonly associated with broad-leaved evergreens. However, it also attacks narrow-leaved evergreens and deciduous species. Plant tissue dries out when there is a vapor pressure deficit between the tissue and the ambient atmosphere. The deficit is generally greatest on sunny winter days when the soil is frozen. Branches may be broken by rain that freezes on them or by the weight of snow. In northern climates, young plants and bulbs planted in fall are subject to heaving caused by alternate periods of freezing and thawing. This is especially true of material planted in clay soil. Finally, winter injury to woody plants can be caused by the depredations of animals, such as deer, rabbits, and mice.
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