Winter is so unpredictable anymore. Snow is pretty, heavy snows and cold temperatures do affect plants as well as humans. Fortunately, most of our landscape plants are well adapted to the snow and cold.
Accumulations of snow can cause severe damage to some landscape plants. Evergreens such as yews, hemlocks, and junipers are especially susceptible to damage from snow. Although wet snow is more hazardous to plants than drier powder snow, any heavy snow can cause problems. Increased weight from snow can cause branches of trees and shrubs to break. Therefore, if you notice your plants weighted down by snow, shake them off as soon as possible with a broom or light rake. Most plants will recover after the weight is relieved, but some could experience longer lasting injury.
Snow is typically safer on plants than ice. The right weather conditions can cause ice to coat all parts of plants, making them very heavy and susceptible to breakage. If ice develops do not attempt to remove it. Ice must melt away naturally. Pruning may be required if breakage does occur. Trees most susceptible to ice damage include those that are topped and those with weak forks and brittle wood such as silver maple, tree-of-heaven, mulberry, and willow.
Cold temperature effects on plants depend largely on the plant itself. Each type of plant has a different inherent tolerance to cold temperatures. Currently our outdoor plants are dormant and resting for the winter. Dormancy allows plants to withstand low temperatures. For example, a maple tree can withstand a temperature of –300F when dormant but may be severely damaged by a temperature just below freezing during the growing season. However, even dormant plants can still suffer during the winter. Extremely cold winter temperatures usually do not kill entire plants, but can kill other parts such as flower buds of some marginally hardy plants including peaches and dogwood.
The good news is that heavy snows and cold temperatures will actually help each other to reduce overall plant damage. Heavy snows insulate the ground and therefore protect low-growing plants and roots from the cold. Roots never really go dormant and cannot tolerate low temperatures like aboveground parts can. Although the top of a boxwood shrub may be able to tolerate –100F, the roots will probably be killed at 200F. Snow cover is an excellent mulch and helps keep roots warm. Snow cover also reduces the likelihood of frost heaving of plants.
Unfortunately, there is little we can do to protect our landscape plants from cold temperatures. It is a wait-and-see situation. We'll find out this spring if significant damage occurred or not. The best way to prevent winter injury is to plant winter-hardy plant material and care for it properly.