Preventing Winter Damage to Plants

Planning ahead can avoid winter damage to trees and shrubs. There are three categories

of winter damage: desiccation, freezing and breakage.

Desiccation, or drying out, is a frequent cause of damage, particularly on evergreens.

Conditions last winter caused significant damage to broad-leafed evergreens such as

hollies, azaleas, rhododendrons and pieris. Injury is commonly seen as discolored or

burned foliage, usually worse on the side facing the wind.

Even in winter, plants transpire or give off water. If the ground has completely frozen or

if the fall has been particularly dry, there may not be enough moisture to supply the roots

of the plant with enough water.

Water loss is greatest during strong winds and mild, sunny weather. The warmth of the

sun can cause stomates located on the lower sides of leaves to open and increase

transpiration. Plants can receive extra damage near a light-colored house, which reflects

the sun’s rays. Small, shallow-rooted or newly installed plants are frequently injured

when freezing and thawing heaves the plants from the soil and exposes the roots to

drying winds.

Small evergreens can be protected by using windbreaks made by attaching burlap, canvas

or a similar material to a frame around the plant. The windbreaks help reduce the force of

the wind and shade the plants. Black plastic should be avoided. The heat builds too

quickly around the plant and causes too much temperature fluctuation at night and the

warmth will cause too much growth too soon in the spring, making the plant more

susceptible to frost damage.

Although the windbreaks protect the plants, they require extra work and are not

particularly attractive. If your plants require this type of protection every winter, you may

want to consider replacing them with hardier specimens or relocating them to a more

protected area. Anti-desiccant compounds are available in many garden centers and

supply catalogs. These compounds are sprayed onto the foliage of the plants and provide

a thin, waxy coating that protects the leaves from the drying winds. The compounds

degrade rapidly and will need to be reapplied during the winter months for best results.

Freezing injuries can occur from fertilization of the plant too late in the fall. The new

growth does not have sufficient time to harden off enough to survive the drops in

temperature. Ice crystals rupture the walls of the plant cells and appear as dead branch

tips.

Milder winter temperatures and warm sunshine can stimulate the opening of flowers or

leaf buds, which are then killed by freezing night temperatures. Freezing injuries can

occur to the roots of plants in containers or planters or to any balled and burlapped plants

that have been left exposed during the winter.

Breakage on plants is usually caused by snow and careless snow removal and the weight

of ice. Winds compound the damage done when ice is on the plant. Snow and ice damage

may cause misshapen plants or cause broken branches and split trunks. By gently

removing snow from plants and by not allowing snow to slide off roofs onto foundation

plants, much damage from breakage can be avoided.

Large temperature changes between day and night may freeze the water in the trunk of a

tree, causing it to split open or explode in a symptom called frost cracking. It is

commonly found on the southwest side of trees where the warm afternoon sun creates

further extremes in temperatures. This can be prevented by wrapping the tree trunks with

burlap strips or commercial tree wrap. Be sure to remove the wrappings in spring.

Understanding certain cultural principles and cultural practices will help to avoid winter

damage to your plants. The right plant in the right place applies once again. Choose

plants that are hardy for your area and choose an appropriate site for them. By planting

holly, azalea, rhododendron and pieris on the north or east side of your home, the plants

will be protected from prevailing winds and intense winter sun. These exposures also

delay spring growth that can prevent frost damage in early spring.

Avoid planting in poorly drained soils so that the water does not freeze around the roots

of the plant. Follow recommended cultural practices to keep your plants healthy. Plants

that are diseased or deficient in nutrients are more susceptible to winter injury than

strong, healthy plants. Avoid late summer or early fall fertilizing as this stimulates late

fall growth that is easily killed by the cold. If desired, fertilize after plants are dormant

but before the soil temperature drops below 45 degrees.

Proper pruning at the appropriate time throughout the year makes a huge difference in

reducing winter damage from ice and snow. Removal of weak, narrow-angled and Vshaped crotches is especially important. Avoid pruning in late summer that can also

stimulate new growth and reduces the supply of nutrients available to the plant through

the winter.

Water properly. If autumn rains have been insufficient, give your plants a deep soaking

before the ground freezes. This is especially important for evergreens. Also, make sure

your plants have a 2 inch layer of mulch to help maintain soil moisture and reduce water

loss. Mulching also reduces the freezing and thawing, which can heave plants out of the

ground.