Winter
Injury
From Cornell University Department of Plant Pathology and Plant Microbe Biology
There are several ways in which the winter environment can adversely affect trees and shrubs. Included are: direct low temperature injury and frost injury; desiccation injury; winter sunscald; frost cracks; frost heaving; and snow and ice breakage.
Direct Low Temperature and Frost Injury: Plants frequently injured by low winter temperatures are those which are planted in areas north of their appropriate hardiness zone. Such species cannot harden off at an appropriate rate or to an extent sufficient to withstand prevailing winter temperatures. However, even hardy plants can be injured during unusually cold periods or when temperatures drop rapidly or oscillate frequently. If hardy plants are not managed properly (not properly fertilized, pruned, watered, etc.) they may also suffer. Flower buds, vegetative buds, branches, stems, crowns, bark, roots, or even whole plants may be injured. Containerized plantings are particularly vulnerable to low winter temperatures since their roots are not protected by being below ground. A result of late spring frosts can be the death of dormant, but particularly, expanding, flower buds on species such as magnolia or lilac, or the death of young, succulent, actively growing shoots. Cold temperature injury that occurs during winter may not be evident until injured tissues fail to grow the following spring.
Winter Sunscald: This type of injury occurs when the sun warms tree bark during the day and then the bark rapidly cools after sunset. These abrupt fluctuations are most common on south or southwest sides of trunks and branches, and they may kill the inner bark in those areas. Young and/or thin-barked trees are most susceptible to winter sunscald.
Frost Cracks: Frost cracks are splits
in bark and wood of a tree that result from rapid drops in temperature. They may be associated with internal defects resulting from previous injury to the trunk years prior to splitting. The strain between the outer, contracting layers of wood and the inner defect causes the outer layers of wood to crack. In winter, the crack may become wider or narrower during colder or warmer periods. Such frost cracks often close and callus over during the summer only to open again in subsequent winters. This callusing and recracking may lead to the formation of large “frost ribs” on the sides of affected trees.
Frost Heaving: Frost heaving of new transplants and small shrubs during the winter will expose plant roots to severe above-ground winter conditions which include cold temperatures and drying wind and sun. Freezing and drying injury to roots, if extensive enough, can result in the death of the heaved plants.
Snow and Ice Breakage/Injury: Heavy snow or ice on weak limbs with foliage (as in the case of evergreens) can result in breakage. Even strong healthy limbs of deciduous trees and shrubs can be broken if the weight of ice or snow is extremely heavy. If the ground is saturated prior to a heavy snow or ice storm, and enough weight is placed on the upper portion of a tree, it can lift the root system right out of the ground.
If you have significant damage to your trees and shrubs, contact Roger 607-535-7161 (rlo28@cornell. edu) for information on how to manage these problems.