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Thursday, Nov. 16, 2006 03:45 pm

Evergreen winter survival tips

Tips for minimizing the stress of cold weather

Untitled Document Although a few of us enjoy cold winter temperatures, most of us can’t wait for 70-degree temperatures to return, and plant species are no different. This winter, as we sit inside our heated homes, let’s not forget about the plants in our landscape. How can we help our plants make it through the winter? Let’s begin this discussion by defining a couple of terms. An evergreen is a plant that has green needle- or scalelike foliage year-round — pines, spruce, yews, and junipers, for example. A broadleaf evergreen is a plant — boxwood, holly, rhododendron, or azalea, for instance — that has green broad leaves year-round. If you expect a plant to survive our winter conditions, begin by remembering the saying “right plant, right place.” Select varieties that are cold-hardy for zone 5, meaning that a plant can withstand low winter temperatures between -10 and -20 degrees Fahrenheit. Match the plant to the site location. Most broadleaf evergreens need a sheltered site, so select a spot that is protected from prevailing winter winds and intense winter sun. The best sites are on the east or north side of a building. Fences or tall hedges of trees or shrubs also provide good protection. Most broadleaf evergreens also need well-drained, moist soil that is rich in organic matter, so you should avoid planting these species under the eaves of a house, where little rain falls. Remember, the more time you spend on site selection and soil preparation, the less time you will need to spend caring for the plants. Another way to help your plants survive the winter is to keep them healthy during the growing season. Diseased, injured, and nutrient-deficient plants are more susceptible to winter injury than their stronger, healthier counterparts. Water is necessary for plant survival, and it is important that trees and shrubs enter winter well watered. Roots will continue to absorb water as long as the ground isn’t frozen. Evergreens and broadleaf evergreens must have sufficient water before the soil freezes in the winter. A tree or shrub that enters winter without adequate soil and tissue moisture is more susceptible to low-temperature injury. If the winter is particularly dry, consider watering on warm days in January, February, and March. One way to help conserve soil moisture and maintain consistent soil temperatures is to add a 2- to 3-inch layer of mulch over a tree’s or shrub’s root zone. This should be done in late fall, after the first indication of frost in the ground. This late mulch application will keep the soil cold and help reduce frost heaving (alternate freezing and thawing of the soil). Winter winds play havoc on evergreens and broadleaf evergreens. Even though these plant appear to be dormant during the winter, they continue to transpire water through their leaves, so the roots must continue to take up moisture from the soil. Desiccation injury occurs when a plant loses more moisture than it can absorb through its roots. You may also have heard the condition referred to as “winter burn” or “winter injury.” Water loss is greatest on sunny, windy days when the ground is frozen or dry and roots cannot uptake moisture. The amount of injury depends on the length of time the stress was imposed. If too much moisture is lost, leaf cells begin to die. Symptoms of excessive water loss in a broadleaf evergreen include browning of the leaf margins, leaf rolling, and a wilted appearance. Injury is worst on the side facing the wind. Other types of winter injury include death or injury to flower buds, the death of a stem, and splitting of bark. Various anti-desiccant products, also called anti-transpirants, are available at garden centers. These products are designed to reduce the transpiration (water loss) of foliage. However, the usefulness of such products is questionable; some research has shown that these compounds degrade rapidly and are not of much value. If you do use an anti-desiccant, read and follow the label directions. Most such products need to be applied before temperatures reach freezing and often need to be reapplied during the winter. With proper planning, winter damage to your plants can be minimized.
Jennifer Fishburn is a horticulture educator with the University of Illinois Extension Sangamon-Menard Unit. Contact her at www.extension.uiuc.edu/Sangamon.
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