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Reduce Damage to Plants this Winter
Martha Maletta, Home Horticultural Consultant
Dated - November 10, 2003
It’s a challenge growing plants outdoors that are not suited to our hardiness zone, but I’ve asked for it. I need to try a new protective tactic for the small fig growing next to my home. Can some of this year’s growth be saved from dieback? Even fully hardy plants can suffer winter injury under certain circumstances, but there are a few fairly simple ways to reduce some types of damage.
Young and newly planted trees and shrubs are generally most vulnerable. Evergreens, especially broadleaf evergreens such as rhododendron, may suffer “winter burn”. (Established plants on sunny and windy sites can also be damaged.) “Burning” (drying out of leaves or parts of leaves) results from a deficit in water supply to roots compared to water demand by the plant, typically occurring under sunny and/or windy conditions with frozen soil. A small root system, as on a recently transplanted plant or plant being grown in a container, can contribute to the problem. Whole plants can die from this desiccation.
To prevent winter burn, avoid sunny and windy sites for the most susceptible plants, and plant evergreens before mid-October to allow for some root regeneration. Make sure the plants go into winter with adequate soil moisture – looks like that won’t be a problem this year – and mulch the soil to conserve moisture. Wind and sun screens can protect exposed plants. Install stakes now and add the screening – usually burlap or canvas – before January. Screening, which should not cover the plant, may only be needed on the south and west exposures. Antidesiccant sprays, available from garden retailers, may help somewhat where screening is not practical, though effectiveness for winter protection has not been conclusively shown. Follow all label directions.
Winter scald is a serious potential hazard for young and thin barked trees. Rapidly fluctuating trunk temperature, typically occurring on sunny, cold days, is the culprit. The cambium layer under the bark, whose hardiness has been reduced by sun warming, is killed by the sudden drop in temperature as shade or night falls. The damage may first be noticed as leaf and branch death next spring. Bark will eventually crack, and insects or disease organisms may invade the damaged area. Frost cracks, vertical cracks on the south or west side of tree trunks, are a related problem. Moderating temperature changes can prevent or reduce winter scald and frost cracks. Use light color tree wrap or other material (not plastic) or tree guards to shade the trunk. Wraps and guards will be removed in the spring. White latex paint is used in orchards for the same purpose but is not as practical for the home landscape.
Roots can freeze when very low temperatures persist and soil is dry and unprotected by snow or mulch, another reason to make sure trees and shrubs, especially newer plantings, are watered and mulched. Container-planted trees and shrubs are especially vulnerable to root freezing since the root mass is above ground. Containers should be insulated or moved to a protected location.
The vagaries of New Jersey winters account for some winter injury, but there is not a lot that can be done to prevent it. Warm fall temperatures can slow cold acclimation that is essential for winter survival, and a sudden onset of cold may result in freeze damage to normally hardy trees and shrubs. Extended warm spells during winter may start to reverse cold acclimation leaving plants vulnerable to damage if low temperatures return.