Winterizing Trees and Shrubs
Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent
Avoiding drought stress with adequate fall irrigation is also important in winterizing your trees and shrubs. Be sure to give your landscape plants a deep watering before your water supply is cut off for the season. Don’t neglect watering the trees, especially birches, situated in your in the lawn.
Fall watering is critical for the broadleaf evergreens, such as rhododendrons, and needled evergreens, such as like pines and arborvitae, in your landscape. They may not be actively growing, but evergreens still lose moisture through their leaves and needles during the winter. They’re prone to damage from winter drought... another reason to keep a hose and sprinklers handy during the winter months. Don’t let them go dry, especially during mild winter weather.
Fall fertilization may also give some protection to trees and shrubs against cold winter temperatures. If you decide to fertilize your plants, place the fertilizer in the root zone area after they have gone dormant, but before the soil in the beds drops below 45 degrees.
Mulching the root zone of trees and shrubs is frequently recommended for weed management and to help reduce the loss of moisture from the soil, but it can also provide some insulation to tender root systems. This is particularly important for plants that are only “borderline” hardy in this region, as well as for young or recently planted trees and shrubs.
Loose mulches can be applied to the root zone to provide some insulation from cold temperatures and to moderate the effects of freezing and thawing. Apply a several inch layer of a mulch material that allows good air and water movement. Use mulches like shredded bark, pine needles, or coarse compost. Keep any mulch several inches away from the trunk of the tree or shrub to discourage mice and to avoid problems from excess moisture close to the base of the plant.
Trunks of young or recently transplanted trees can be protected against splits by shading the south and west sides of the trunk. Some gardeners shade the trunk of their trees with a commercial bark wrap or they simply use a board on the sunny sides. The shading or wrap keeps sunlight off the trunk, preventing the bark from warming up too much on a cold winter day and reducing temperatures fluctuations that can lead to trunk or bark splitting.