Prevent Winter Damage to Trees and Shrubs

If extreme winter weather has ever taken a toll on your landscape plants, you aren't alone. Every spring, gardeners in regions hit by a tough winter discover the damage it can cause to trees and shrubs. Fortunately, you can take steps in autumn to prepare plants for what's coming.

Extreme cold isn't the only challenge faced by woody plants; in fact, plants hardy to your region should endure normal winter temperatures just fine. However, winter can wreak havoc in other ways.

Winter Challenges

• Early cold spells can damage plant tissues that haven't had a chance to harden off for the winter.
• Dry winds and winter sun can dry out or "burn" conifer needles and broadleaf evergreen foliage, which continue to transpire (give off water vapor) during winter.
• Frozen soil means plants can't take up water to replace the moisture lost from evaporation and transpiration.

• Midwinter thaws can "fool" plants into breaking dormancy too early, and the tender new growth may be killed by the next cold snap.
• Alternating freeze/thaw cycles can heave new plants out of the ground, leaving roots exposed to drying wind and sun.
• Bright winter sun heats up dark tree bark, which can freeze and crack when temperatures drop quickly at sunset.
• Deer, mice, rabbits and other animals gnaw bark and browse leaves and twigs when other food becomes scarce during long, cold winters.

Although wet, heavy snow can damage branches, snow cover is usually good for plants. A layer of snow provides moisture and helps insulate the soil and roots from fluctuating temperatures.

Preparing for the Big Chill

Healthy plants are more likely to get through winter unscathed. A plant that has struggled during the growing season, whether due to insufficient sunlight, water or nutrients, or heavy damage from insects or disease, will enter winter in a vulnerable state. Start your winter-protection strategy with careful care during the growing season and into autumn.

• Don't prune after midsummer. Pruning stimulates tender, new growth and delays dormancy.
• Stop fertilizing plants six weeks before the first fall frost, to help plants harden off properly.
• Water plants thoroughly throughout fall until the ground freezes; make sure the water penetrates 12" to 18" deep to reach the root zone.

Here are tips for specific types of plants:

Deciduous Trees and Shrubs

Deciduous shrubs and trees — those that lose their leaves in autumn — have adapted to life in cold-winter climates by going dormant. Many of these techniques are designed to ensure that plants enter dormancy before the coldest weather arrives, and remain dormant until spring.

Mature trees and shrubs that are hardy in your region need no extra protection. However, young and newly planted trees and shrubs benefit from some extra TLC:

1. Because plant roots may not have ventured very far into the native soil, it's especially important to water newly planted trees and shrubs thoroughly into fall, until the ground freezes.
2. Once the ground is frozen, apply a 3" to 4" layer of insulating mulch, such as bark mulch or pine straw, around the base of the plant. This helps insulate the soil so it stays frozen and helps prevent heaving. Keep the mulch several inches away from the trunk to prevent rot and discourage rodent chewing.
3. Tender young bark is easily damaged by gnawing mice and rabbits. Protect the trunks of young trees — especially fruit trees — with tree guards made of plastic or wire.
4. The bark of young trees is also susceptible to sunscald. Paint the south side of the trunk with a solution of diluted white interior latex paint or wrap the trunk with paper tree wrap. This also helps prevent frost cracks, which occur when dark-colored bark heats up on a sunny winter day and then rapidly cools at night.

You can find tree wrap and guards at garden centers and hardware stores.

Conifers and Broadleaf Evergreens

Trees and shrubs that remain green — conifers and broadleaf evergreens, such as rhododendrons — slow their growth but never go fully dormant. It's especially important that they have a ready supply of water whenever the ground isn't frozen.

1. Drying winter winds are especially damaging to evergreens. In exposed, windy areas, erecting a windbreak helps prevent damage, as can wrapping shrubs with burlap or easy-to-use shrub wraps.
2. If branches are bending under the weight of a heavy snowfall, gently remove some of the snow. However, don't try to remove ice after an ice storm; you're likely to cause more harm than good.
3. Some evergreens, notably white pines, are susceptible to damage by road salt sprayed onto branches by passing snowplows. In spring, you'll see brown needles on the road-facing side of the tree. Protect hedges and shrubs with burlap or shrub wraps. On taller trees, there is little you can do; consider replanting with more salt-tolerant species.
4. Keep deer from browsing on hedges and shrubs by wrapping them with burlap or shrub wraps.