As we anticipate the arrival of "old man winter," it often seems hard to believe that our landscape trees and shrubs can survive the rigors of the cold winter months. Extremely low temperatures, frozen soil, rapid temperature changes, drying winds, or lack of soil moisture all may work individually or together to make plant survival a challenge. Even with our best efforts, some damage is possible. However, gardeners can reduce the chances of damage developing by following 10 simple tips.
- When adding plants to the landscape, use only plants that are well adapted to the climate. The USDA plant hardiness zone map (https://planthardiness.ars.usda.gov/) can be very helpful in determining the average low temperature expected in your area. Native plants are good choices, since they have naturally acclimatized to local climatic conditions. However, dependable plant selections may be made from other areas of the world with climatic and soil conditions similar to where you live.
- Plant trees and shrubs in well-drained soil unless the plants in question have adaptability for poor drainage. One of the most damaging conditions in winter that weakens plants is poor drainage. A simple way to measure drainage is to dig a hole one foot deep and fill it with water. Allow the water to drain through the soil. Then, refill the hole and, with a ruler, measure the water depth immediately after refilling and one hour later. A drainage rate of between one to three inches per hour is considered adequate for most plants.
- Whenever fall weather has been dry, water trees and shrubs well before the soil freezes to ensure adequate soil moisture to carry the plants through winter. Even dormant plants without leaves continue to lose water during the winter through their bark and twigs. Water loss is increased under windy conditions. When the soil is frozen, the availability of water is reduced. If soil water is deficient as winter begins, damage tends to be more severe.
- Mulch around the base of trees and shrubs. This will increase moisture retention and decrease the depth of the frost line. Mulches also prevent alternate freezing and thawing of soil as air temperatures fluctuate, which can result in frost heaving of shallow-rooted species. Mulches should not be piled up against the trunks of trees or shrubs (sometimes called "volcano mulching") which tends to promote disease and prevent proper cold hardening of tissue as temperatures during the winter drop.
- Unless they can be moved inside or otherwise protected during the winter, do not plant small trees or shrubs in containers. The roots of woody plants are more susceptible to cold temperature injury than their shoots. Containers are exposed to the cold air on all sides and lack the insulative effect of soil. The result is the winter soil temperature inside an above-ground container can be very close to air temperature, which often results in loss of a plant's root system.
- Wrap the trunks of newly planted or thin-barked trees with tree wrap or other materials such as spiral plastic protectors. This practice will reduce the chance of winter sunscald or frost cracking of the trunk by discouraging abrupt temperatures changes. Continue this practice until trees are three to five years old, depending upon species. Trunk wraps also help to prevent damage from rodents such as rabbits, voles, and mice which feed on tree bark during the winter.
- For newly planted or marginally hardy evergreens, construct canvas, burlap or slatted windbreaks on the south and west sides of exposed plants to prevent sunscald and desiccation. Screens should be two feet in distance from the plants and tall enough to shade them from the winter sun. In areas with strong prevailing winds from the north or northwest, it might be advisable to construct windbreaks that surrounds each plant. For plants such as azalea, filling around the stems in the enclosure with a loose mulch can provide additional protection.
- Anti-desiccants also provide some protection for broad-leaved evergreen or for newly planted trees and shrubs. In some areas they can serve as a substitute for windbreaks. Temperatures must be above 40 degrees F when application is made and must be repeated every six to eight weeks during the winter. In areas with strong winds, anti-desiccants should be applied to cover stems and branches as completely as they are to the leaves or needles of the tree or shrub.
- Tie branches of multi-stemmed evergreens together with a strong, pliable cord to prevent ice or snow from disfiguring or breaking the plants. Plants that become covered with snow normally are better off being left alone opposed to attempting to remove the snow layer via shaking or raking. The latter often does more harm than good because of the brittle nature of frozen wood.
- In early spring, as soon as any winter damaged branches or twigs can be detected, prune them out. Painting of tree wounds with dressing is not necessary. Application of a complete fertilizer in March or early April can help to stimulate new growth and repair wounds of damaged plants.
Trees and shrubs are an important part of the landscape and often represent a significant investment. Both the investment and appearance of the landscape can be protected by following a few simple rules before the wrath of winter is upon us.