Earlier this week, people across Georgia were greeted with bitter cold temperatures in the teens as they headed back to work and school after the New Year's holiday. And while such frigid weather is difficult for us, it is equally tough on many of our landscape plants — including even the toughest trees and shrubs.
Cold weather can cause all types of plant problems. Freezing temperatures can damage plants by rupturing plant cells as ice crystals form. Evergreen plants can suffer damage from blowing winter winds and dry out when water is unavailable from frozen soil.
The signs of cold damage can be confusing, since some damage may not be evident until months later. Leaves and tender shoots subjected to freezing temperatures appear water-soaked and wilted. These tissues will usually turn black within a few hours or days. This damage may not be evident until spring when there are fewer flowers.
Even the hardiest of plants may experience bark splitting, which typically occurs near the base of the plant due to sudden changes in temperature. If damage occurs at the crown (base) of the plant, it may not survive. Split stems and branches should be pruned to unaffected growth.
Frost cracks are also common following a deep freeze. A frost crack is a long, deep, narrow crack running up and down the trunk of a tree. The crack is usually on the south or southwest side of the trunk, but can occur on any side. Young trees or older trees with smooth bark are the most susceptible.
Frost cracks occur when the sun warms the trunk in the winter, causing tissues to rapidly expand, or when clouds or buildings block the sun. At sunset, the temperature of the trunk drops quickly to that of the surrounding air, and the trunk contracts. The outer part of the trunk cools and contracts faster than the inner tissues. This difference in contraction rates can cause the outer trunk to crack.
Tree trunks can be protected by wrapping them with paper tree wrap or burlap to prevent frost cracks. The wrap should start at the ground level and go all the way up to the first main branches. Prevention is important, since once the crack occurs nothing can be done.
Desiccation, or drying out, is a particular problem on evergreen plants. This occurs when water is leaving the plant faster than it is being taken into the plant. During the winter months desiccation can occur if the ground is frozen beyond the depth of the root system. This type of injury appears as discolored or burned evergreen needles or leaves.
Following cold damage, don't be in too much of a hurry to prune or remove your damaged plants. Some plants may appear dead, but they are not. Corrective pruning should not be started until the full extent of the damage is determined.
Injury to foliage and tender shoots should be visible within a few days, but it may be several months before damage to larger limbs can be determined. Wait to see if any live green foliage reappears or gently scrape under the outer layer of bark to see if green wood is present.
Once you have determined the extent of damage, remove any dead wood. There is very little that can be done to revive plants suffering from the extreme effects of freezing. Contrary to popular belief, watering cold-damaged plants that appear wilted will not help to revive them.
Bottom line — hang in there! Spring will be here before we know it, and with it comes the fine gardening weather we're all waiting for!
Billy Skaggs is an agricultural agent and Hall County extension coordinator. Phone: 770-531-6988. Fax: 770-531-3994.