Avoiding Winter Damage
5 November 2007
Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580 fax: 434.872.4578
It is often necessary to give a little extra attention to trees and shrubs in the fall to help them overwinter and start spring in peak condition, especially if you are planting them in the next few months. This year is no exception and with the recent drought combined with the predicted slightly warmer temperatures and slightly lower precipitation, this winter may require more effort than usual. Understanding certain principles and practices will significantly reduce winter damage to woody ornamentals.
The majority of winter damage can be divided into three categories: desiccation, freezing, and breakage. Desiccation, or drying out, can be particularly damaging to evergreens, causing discolored or burned foliage and even plant death. Leaves continue to transpire in the winter, though at a lesser rate than in the summer. Winter winds can increase the rate of transpiration, causing the plant to dry out, particularly if the ground is frozen and the plant cannot take up more water.
Freezing damage most commonly occurs in the fall or spring, when green wood (new growth) or blossoms are susceptible to sudden frost. Mid-winter freezing often takes the form of bark splitting. On a relatively warm day, the sun can really heat up dark-colored tree trunks and get the sap flowing. If a severe freeze occurs that night, the bark may split.
Breakage is usually caused by a combination of ice, snow, or wind. The weight of ice and snow can break even large, strong branches, especially if the wind further taxes the physical strength of a plant. Another cause of breakage is improper removal of ice and snow. Frozen, laden limbs are very brittle and snap easily if bent the wrong way.
Much of the disappointment and frustration of winter-damaged plants can be avoided by planning ahead. Start off by selecting hardy plants. Grow plant materials that are either native or are known to be winter hardy in your area. Select an appropriate site for more tender specimens. This means a site with well-drained soil, not exposed to winter wind and sun (north, northeast, and east sides of the house), and away from eaves where falling snow may break branches.
Follow recommended cultural practices. Avoid late-summer or early fall fertilization that may stimulate new growth for frost to kill. Fertilize in late fall and use slow release materials so the plants can use the nutrients to keep up their strength over the long haul rather than putting on new growth now. Avoid late-summer pruning, as this also stimulates new growth, but keep the plants properly pruned at appropriate times to remove weak branches with narrow crotch angles. Water plants deeply in preparation for winter and especially soak evergreen plants. Also plan to water your woody ornamentals deeply on warm days in January, February, and March.
Mulching reduces water loss and soil heaving while allowing the roots a little more time to grow in the fall. Leave several inches of bare ground between the trunk and the mulch to discourage mice from nesting and feeding on the bark.
Remove snow before it can accumulate by sweeping the branches UPWARD with a broom to lift off the snow without further stressing the limbs.
Shade trunks of young trees with a board or wrap in cloth or paper to reduce the chance of bark splitting. Bark splitting is caused when dormant trees are coaxed into cambial activity on warm winter days, especially when trees are exposed to direct sunlight. When freezing temperatures return, the active cambial tissue is killed, causing the frozen bark to separate from the wood of the trunk. The shading of the trunk prevents the bark from heating up to begin with, so it prevents bark splitting from occurring.
Registrations for Master Gardener Volunteer training classes are being accepted in Albemarle, Fluvanna, and Louisa Counties. Please call your local Extension office if you are interested.
For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.