Winter desiccation is a common type of winter injury that occurs when the amount of water lost by a plant exceeds the amount picked up by the roots; other common terms for this type of injury are winter burn, winter drying or winter scorch. It occurs when the soil is frozen and plant roots are unable to pick up enough water to meet the needs of the plant. Warm, sunny days or windy conditions increase the amount of water lost through leaves and needles, and increase the severity of winter desiccation. This spring many plants are showing signs of this environmental problem.
Evergreen plants are particularly prone to winter desiccation because they hold their needles throughout the winter and use water at a higher rate than deciduous trees. When water usage exceeds available water, the needles, leaves and twigs dry out and die. Usually evergreen leaves or needles hold their green color even after the injury has occurred until warm spring temperatures arrive, resulting in delayed browning symptoms. Affected needles turn yellow or reddish-brown at the tip, and dieback to the base.
Often the pattern of damage is directional, on one side of the tree more than the other. Wind accompanying dry periods can accelerate water loss from the plant and result in damage that is more extensive on the side of the tree facing the prevailing wind, particularly those with southern or western exposures. If damage is very severe, the entire plant may turn brown and die.
Another factor that can contribute to a directional pattern of browning is solar radiation reflected from hard surfaces such as brick siding, pavement, light-colored metal siding or white lava rock mulch. Evergreen trees planted along streets may show browning of the foliage nearest the roadway. Foundation plantings of yew, juniper, dwarf Alberta spruce and arborvitae located around buildings show browning on the side next to the house.
Factors that can predispose plants to winter desiccation are poorly developed root systems due to improper planting, root injury, girdling roots, soil compaction, fall drought stress or stress due to insects or disease and tree genetics, i.e., trees from a southern United States source.
Evergreen trees with a small amount of needle loss may still have live buds within the damaged branch sections. These buds will send out new growth and eventually fill in the damaged section in a few years. Evergreen shrubs, like holly and mahonia, may regenerate new leaves to replace the damaged foliage if injury was not severe enough to kill the underlying branches. Wait until new growth has emerged before pruning out dead branches.
This summer provide plants damaged by winter desiccation with one inch of water per week, allowing them to growth vigorously and avoid further injury next winter. Add 3-4 inches of organic mulch, such as wood chips, over the root system of susceptible plants in fall to conserve soil moisture. Susceptible trees and shrubs may be protected from prevailing winter winds next year by erecting a lath or burlap screen on the south or southwest side in fall, or by transplanting them to a more protected location.
Sarah Browning is a Horticulture Extension Educator with University of Nebraska- Lincoln Extension in Dodge and Saunders Counties. She can be contacted by phone at 727-2775: by mail at 1206 W. 23rd Street, Fremont, NE 68025: or by e-mail at sbrowning2@unl.edu
