Coping With Winter Tree Injury

Problems to Look for in a Tree During and After Extreme Cold

Snow coated trees in Siberia
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Damage to Trees During Cold Weather:

Winter tree damage can occur from any of a long list of cold related problems. You can avoid these problems by picking a good site with stable temperatures and by winterizing your tree. You need to realize that tree injury is not generally caused by an unusually cold winter, but from extreme temperature fluctuations and the timing of these cold weather extremes during the dormant period and into the growing period.

Here are the most common causes of winter tree damage:

Extreme and Rapid Temperature Changes:

Trees much prefer slowly falling temperatures and a period of acclimation. Trees that are dormant but not fully acclimated can be stressed or injured by a sudden, hard freeze. Wild drops in temperature following mild weather can cause injury to woody plants. Extended periods of mild winter weather can cause a tree to resume growth making them vulnerable to injury from rapid temperature drops.

Low Temperature Injury and "Frost Crack":

Frost injury can occur when a tree is growing during early fall or late spring and a freeze injures or kills vulnerable tree tissue. To avoid frost damage, plant locally adapted trees, cover trees if frost is expected, avoid frost-prone sites and lay off nitrogen fertilizer at the end of the growing season. "Frost crack" can cause serious damage to trees by lengthening already existing wounds after repeated freezes.

Winter Injury Called Sunscald:

Winter burn is a common conifer problem. Rapid temperature change on the south side facing the sun can cause needles to burn. Drying is caused by warm conditions taking tree moisture while frozen ground and tissue restrict plant water flow. Planting hardy trees, mulching, wrapping and avoiding areas with sudden temperature can help.

Sunscald can occur in late winter or early spring when the temperature is above freezing during the day and below freezing at night. Shading or wrapping can help.

Chemical Injury from Deicing Salt:

Salts used for deicing pavements can cause damage to trees and shrubs. Symptoms of salt damage appear in spring and early summer and include browning of evergreens, leaf scorch, and branch die back. Salt will leach through well-drained soils and have little to no effect on trees. Poorly drained soils present the problem so choose salt-tolerant species for sites where salt stress may be a problem and where salt can accumulate from poor drainage.

Late Spring Freezes:

Once spring tree growth has begun, a late spring frost can cause damage. This is especially harmful if the freeze takes place after an early spring warming period. Succulent, new tree tissue turns flaccid, appears water-soaked, and withers within a short time. The symptoms of a severe late spring freeze resembles several diseases. Freeze injury appears suddenly after a hard frost while diseases generally occur throughout the year and take much more time to develop.

Frozen Roots:

This type of damage is usually associated with newly planted seedlings and container grown trees and only after freezes that extend over a long periods of time.

Shallow rooted trees and shrubs are vulnerable but can be protected with mulch, leaf litter, or snow cover. These "covers" insulate the roots sufficiently to prevent soil temperatures from staying below freezing for long periods. Plants with frozen roots may wilt and decline after growth resumes in the spring.

How to Minimize Winter Tree Damage:

- Select hardy species and cultivars.
- Avoid late season fertilization.
- Keep trees and shrubs watered during dry periods.
- Use mulch to retain moisture and to insulate roots.