Concerned About Cold Damage

— Written By Peg Godwin and last updated by
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Cold damage is not easy to predict. Plants damaged from the cold may lose early flowers, have a visible marginal leaf burn, have water-soaked tender shoots that progress to black tissue, have tips that are uniform brown or appear dead. Bark splitting and frost cracks are also frequent types of cold damage. The plants, which survive extreme temperatures, may be seriously weakened increasing their susceptibility to borers, cankers, and other problems over the next several years.

Extremely cold temperatures are not usually the cause of the plant injury. It is the combination of fluctuating temperatures along with factors of plant health and care that usually cause damage. Acclimation is the term used for the adjustment plants make over time to tolerate cold temperatures. It is the sudden changes in temperatures that cause the most damage. Mild winter days with temperatures in the upper 60s or 70s followed by a sudden drop into the 20s, does not give the plant time to adjust.

Some cold damage is unavoidable but here are a few steps to limit injury. Avoid pruning in late summer or early fall. Pruning at this time of the year can make plants more susceptible to injury. Plants respond to pruning by producing new growth that does not have time to harden off before cold temperatures arrive. Pruning should be completed by the end of July and not begun again until late winter.

Do not apply fertilizers in fall or winter that contain nitrogen which encourage the production of tender new growth. Nitrogen applied in late summer can also increase winter damage. Potassium increases a plant’s ability to withstand the cold. Use a soil test to determine if your soil is low in this nutrient.

Plants growing in containers are more susceptible to cold damage as the roots do not have protection of the soil. Plants can be covered with fabric or mulch or packed tightly together for protection during sudden cold temperatures.

Water loss is a major factor in winter injury and is greatest during sunny windy days. The water needs of plants should be met prior to a predicted cold snap. Moist soil absorbs more heat that dry soil.

Cold damage to foliage and tender shoots is visible long before damage to larger branches can be determined. Do not quickly prune damaged plants. Corrective pruning should not begin until freezes have passed to guard against removing living wood. Branches can be checked for live wood by gently scrapping off the outer layer of bark to see if green wood is present underneath. Test a plant bud for damage by cutting a cross-section through the tip with a sharp knife. Discoloration is the evidence of damaged tissue. It is best to prune several inches below injured tissue.

It is hard to be patient and wait to see what needs to be done to a damaged plant. Do not act too quickly to determine how plants have faired during the cold temperatures.