Winter Injury to Trees and Shrubs

Your outdoor landscape plants face a number of environmental problems in the cold weather areas of the country including winter injury, sunscald, and tipburn. It may not be possible to escape some winter damage, but there are ways of reducing risks.
Winter Injury - Winter injury occurs to many landscape plants during subfreezing temperatures, especially when the water in the soil is frozen, making it unavailable to be absorved by the roots. Plants continue to transpire water from their leaves, especially if it is sunny and windy. When more water is transpired than the plant can absorb, desiccation occurs. That is the excessive drying up of leaves and plants parts which can be very harmful to the plant. Winter injury is more common on broad-leaved evergreens such as azaleas than it is on conifers or deciduous plants. Preventive measures include watering the plants well before the ground freezes, spraying with an anti-transpirant, and mulching and protecting the plants from drying winds and bright sun while the ground is frozen. See Chapter 8 for more details about winter protection of landscape plants.
Sunscald - Sunscald may sound like something that happens in hot weather, but it is a wintertime problem. It is particularly noticeable on young trees planted where daytime heat is high, such as beside a wall that reflects the sun's heat. Tender bark on a southern surface warms much more than on a northern surface. The temperature of dark-colored bark is raised considerably by the sun's rays, but if a chilling breeze comes along or a cloud suddenly covers the sun, the mercury falls rapidly. The sudden change makes the cells rupture, and the bark splits open. Diseases and insects may enter the splits and cause further damage. Sunscale on trees can be prevented by wrapping the trunks with a commercially available tree wrap or with burlap or agricultural fleece. Some homeowners guard against early-spring sunscald by spraying the bark on the south side of the young trees with white latex paint in the fall. The light color reflects the sun's rays and prevents sudden temperature changes .
Tipburn (or windburn) - Tipburn is a result of drying by sun the wind, usually appearing on the west or southweast side of an evergreen shrub. Although the damage occurs in the winter, there may be no sign of trouble until spring. Then the tips of leaves or needles turn brown, and in severe cases whole leaves or the ends of affected branches die. To prevent tipburn, water well in the fall and apply a heavy mulch. Protect vulnerable shrubs with a windbreak of stakes and burlap, or shelter with a pile of brush. See Chapter 8 for more information about winter protection.
Winter Dieback - Winter dieback is the equivalent of tipburn in deciduous plants. It is a particular problem with shallow rotted plants such as young trees and deciduous shrubs suich as viburnum. As with tipburn, the damage may not become noticeable until spring. Branch tips that were healthy in the fall will appear dead. To check for damage, scrape away a small patch of bark on the affected twig. If the twig's alive, the underbark will be bright green. If it is dead, it will be black. Fall watering and good mulch will prevent dieback.