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Protect your trees, shrubs this winter

November 16, 2012 12:10 am

WINTERIZING trees and shrubs will help them survive the winter and welcome spring in peak condition.

Desiccation and freezing are common sources of winter damage, but there are some simple ways to limit the potential for damage.

Desiccation means drying out and it is a particular problem for evergreens. Desiccation occurs when water leaves a plant quicker than the plant's roots can take up water.

Evergreens transpire and loose water through their needles and leaves during the winter. The loss is greatest on days that it's mild, sunny and windy. Even if the air temperature is cold, the temperature inside the leaves may be warm. The sun's heat causes the stomata, or pores, on the underside of the leaves to open, increasing transpiration and water loss. Root uptake of water is reduced or prevented when the ground is frozen or just very cold.

The foliage of plants may turn yellow or orange due mild desiccation or excessive sunlight. When the injury is more severe the plant will have discolored, burned evergreen needles and leaves. Branches can dehydrate and die in extreme cases.

Watering and mulching can help reduce desiccation injury. A 2- to 3-inch layer of mulch will help maintain uniform moisture and temperature around the roots. Water plants regularly during the winter to maintain soil moisture levels, the moist soil will absorb more solar energy and will release heat during the night.

Anti-desiccant products can be applied to help reduce water loss. However, these products degrade quickly and need to be reapplied often in order to achieve sustained protection.

A plant's location within the landscape can impact the injury risk level. Plants located on the north, northeast and east sides of buildings have better protection from the sun. Delayed spring plant developments in these northerly exposures helps prevent injury due to late spring frosts. A south side location with no shade or wind protection is the location of greatest risk.

Shade and windbreaks can also provide protection. Plants that freeze and thaw slowly are less prone to injury. Plants can be protected by building frames over the plants and covering the frames with burlap. The covering material should not touch the plants because contact between the leaves and the covering can accelerate leaf heat loss. Windbreaks can be built by attaching burlap or canvas to a two- sided frame.

Injury from freezing takes two forms. Bud growth that in stimulated by late summer or fall fertilization is prone to freeze damage because young buds have not had enough time to harden off prior to cold weather. Ice crystals that form within these buds rupture cell walls.

Discolored leaves and dead branch tips are signs of this damage, which can be prevented by delaying fertilization until after the plant is dormant.

The other is "southwest injury" or frost crack injury. This is caused by sharp temperature changes that can freeze water within the trunk or branches causing splits called frost cracks. Mild frost crack injuries may appear to close when warm weather occurs, but the damaged wood fiber may not grow back together.

The term "southwest injury" comes from the fact that the southwest side of young plants is more prone to the damage because the warmth of the afternoon sun creates further extremes between day- and nighttime temperatures.

Damaged branches and areas can be pruned out of the injured plants in the spring. Damaged plants may be delayed in starting new growth, so wait to wait until after new spring growth starts to assess the damage. Broadleaf evergreens with leaf injury can start growing new leaves if the branches and leaf buds have not been too severely damaged.




John E. Howe is an agent in Virginia Cooperative Extension's Spotsylvania County office specializing in animal science. Phone 540/507-7571; email jhowe@vt.edu.




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