Addressing winter problems with trees and shrubs
By Susan Edwards CHESTERFIELD COUNTY COOPERATIVE EXTENSION

LiLi Ferrel (left) and Chris Lumpkin, both county groundskeepers, spread mulch around a tree at the government center. Mulch helps soil retain moisture.

In my short five and a half years here in Virginia, I have learned one thing about the seasons here: they are unpredictable. We can have snow on a Wednesday and be back in the 60s on Saturday. And just because it's January doesn't mean an 80-degree day is out of the question, nor is dipping into the 20s at night in late September.

Drastic changes in temperature can impact ornamental plants - even very short events can cause damage. Desiccation, sun scald, freezing and breaking are the most common types of damage that occur in the winter months, and we collectively refer to these types of damage as "winter injury." Winter injury may be superficial, or it can be detrimental to the health of the plant. Here is a short list of the most common winter problems, how you can prevent them and what you can do after damage is done.

Desiccation

Winter foliage desiccation is akin to our skin drying out in the winter: moisture is removed from the foliage faster than it is replaced, which results in discolored, burnedlooking foliage, especially at the edges of leaves. Desiccation is notorious in evergreen plants and can occur as the result of winter winds or sunny, mild winter days. The heat of the sun can cause leaves to increase transpiration (the releasing of moisture), but moisture uptake remains at the same level. Even though the air is warm on the surface of the leaves, the soil is still very cold - the roots will not acquire water from the soil as quickly as the moisture is lost to the atmosphere through the leaves. Proper watering is crucial to reducing damage, especially when fall rains have been insufficient like this year. You can water plants on warm days throughout the winter. A good layer of mulch around your ornamentals will also help preserve soil moisture, as roots can also dry out if not properly protected.

Sun scald

Warm afternoon sun on the bark of trees and shrubs can cause damage known as sun scald (also called bark crack, frost cracking or southwest injury). Cells that have been warmed by the afternoon sun rupture once temperatures drop at night, causing the bark to split. This problem will usually correct itself, and the wound will close over. You can prevent this type of damage, especially on young ornamentals, by wrapping the trunk with strips of burlap or tree wrap to reflect the sun's heat during the day. Be sure to remove these wrappings in the spring.

Other freezing injuries

Warm sunny days can cause flower and leaf buds to open prematurely and be killed by subsequent freezing temperatures. Plants left in containers or balled and burlapped over the winter can sustain root damage and should be placed in protected areas, heavily mulched or sunk into the ground for protection.

Breakage

The weight of snow and ice can cause limb breakage, but so can the manner in which people removed the snow and ice from the branches. Always push upward with a broom to remove snow - don't brush downward. Leave ice in place, as breaking frozen branches can cause more damage to the plant than the ice itself. Warmer temperatures will eventually melt it away. Properly pruning trees and shrubs can significantly reduce breakage in the winter months.

More information

Helpful tips on pruning as well as pruning calendars are available through the county's extension office. More information on this topic can be found in VCE Publication 426- 500, "Managing Winter Injury to Trees and Shrubs." Contact the Chesterfield County Cooperative Extension Office at 751-4401 to request a copy, or visit online at www.ext.vt.edu/resources/anrpublications.html.