The Effects of Frost or Cold on a Tree

Tree Tolerance

• Trees have natural mechanisms to avoid and tolerate freezing, the Warnell School of Forestry and Natural Resources at the University of Georgia reports. Tree bark provides insulation between the cold, outside air and the warm, moist wood inside of trees. A tree's foliage and canopy act as shields against freezing. Trees also avoid freezing by developing a tolerance to dehydration through a process called hardening, which begins when days grow shorter in late summer. During hardening, tree membranes and processes change so cells force water out of themselves. Water removal from cells is crucial, because ice crystal formation punctures cell membranes and crushes cells. If cold weather arrives before hardening is complete or if temperatures fluctuate, injury to trees can occur.

Frost Heaving

• "Frost heaving," caused by the repeated freezing and thawing of soil, causes trees, particularly young trees, to lift out of soil. As a result, thin feeder roots can break or dry out, injuring or killing the tree. Frost heaving occurs more often in heavy soils, the University of Purdue Cooperative Extension Service notes. Trees that are properly watered, fertilized and protected from pests during growing season develop more extensive root systems, which survive heaving better. Snow cover or a thick layer of organic mulch helps to prevent heaving.

Frost Cracking and Sunscald

• Frost cracking and sunscald occur under similar conditions. Damage is typically located on the south or southwest side of tree trunks, where most sun occurs. A frost crack is a long, deep, narrow crack running the length of the trunk. Cracks occur when the sun warms the trunk, causing interior tissues to rapidly expand, but the bark contracts more quickly when it becomes cold again. The trunk might even be heard cracking. Sunscald occurs when the sun heats tree bark during the day, and the bark experiences rapid cooling after sunset. This causes long, sunken, dried or cracked areas of dead bark. Cracks allow damaging pests into the tree. According to the University of Vermont Extension, the most effective way to prevent these injuries is to wrap tree trunks susceptible to frost cracking and sunscald with protective "tree wrap" available at garden centers.

Dessication

• Evergreens, particularly, can suffer from winter dessication injury, which occurs when plants lose water from their leaves faster than it can be replaced by roots in frozen soil. Plants lose water more quickly on sunny days, particularly when it is windy. Injured trees show brown leaf margins or needle tips at the onset of warm weather in spring. Severe dessication can kill leaves and buds. Watering trees well in fall and early winter helps to prevent winter dessication, says the Purdue University Cooperative Extension. Placing burlap over or around plants to protect them from winter winds and sun also offers protection.

Damaged Buds

• Fruit trees require some cold winter weather to spur spring growth. But extreme cold during winter, such as temperatures near -10 degrees Fahrenheit, can kill fruit buds of less hardy fruits varieties, such as peaches, according to the Washington State University Cooperative Extension. As all fruit buds open, they become susceptible to injury from frost.