Reprint: Country Wisdom News 2010
Winter weather can damage landscape plantings. Freezing temperatures, wind, and winter sun can desiccate foliage, damage bark and vascular tissue, and injure root systems and branches.
Temperature extremes and fluctuations can harm plants. Typical winter injury is desiccation of foliage due to moisture loss when the soil is frozen and plants cannot replace the moisture that was lost through transpiration. Browning and in some cases dropping of foliage in early spring are signs of damage.
Anti-desiccant treatments protect evergreens from sun and wind overexposure by sealing in moisture. Water plants before soil freezes and apply a layer of mulch around trees to maintain soil temperature and retain moisture. Wrap susceptible trees in burlap during winter to reduce loss of water through the leaves.
Trees are deceived by the warm temperatures of late winter and emerge from dormancy, only to have tissues killed when winter temperatures return. In broadleaves, freeze damage can be recognized by reduced leaf area in the crown, branch tip dieback, clumped leaf growth, or death of the main stem with new sprouts growing from the base of the tree. In evergreens, symptoms include loss of buds, drooping of branches, lack of new growth, and dieback. There is no protection from this injury, however well cared for trees and shrubs recover faster.
An early frost in the fall or late spring frost when plants are actively growing may damage plants, causing leaves and shoots to be injured or killed. Most healthy trees recover from this damage. Years of repeated frost exposure reduce growth as energy is used up to replace damaged tissues.
Some tips for protecting your trees and shrubs include:
• Plant tree species hardy to conditions in your area.
• Cover young trees if frost is expected.
• Avoid planting in areas subject to frost.
• Don’t apply high-nitrogen fertilizer late in the growing season.
Thin-bark trees or transplanted trees are most affected by sunscald. Direct sun during midwinter heats south or southwest facing bark to above freezing, causing cells to become active. When the sun sets or bark temperature drops with changing weather conditions, the active tissue is frozen and killed. Patches of bark crack and fall off, forming a canker. Cankers are susceptible to insect infestations and disease during the next growing season.
Wrap the trunks of susceptible trees or shade them in winter to help prevent sunscald. Cracks or bulges on trunks begin at the site of wounds or branch stubs. Sudden drops in temperature can cause the outer layer of the trunk to contract faster than the inner layer of tissues, leading to an extended crack.
To decrease the chances of developing cankers, avoid wounds to the trunk and properly prune branches to prevent the formation of cracks. Wrap the trunks of young trees with paper tree wrap to prevent cracks.
As food supplies are reduced, rodents and deer may turn to the new stems or bark of trees for their next meal. This feeding on the plants can cause them to weaken or die. Damage control measures could include repellents, physical barriers, and ultrasonic protection.
Those plants that are properly selected for their site and well maintained throughout the season will fare best through the winter. A few good tips to follow include: good cultural practices, watering during dry periods, controlling insect and disease issues, and tying plants such as yew, arborvitae, and juniper that may be damaged by the weight of snow.
Have your trees inspected each year by a qualified arborist. To locate a qualified arborist in your area, visit treesaregood.org.
Peter R. Landau is an ISA Certified Arborist.