December is upon us and so are winter temperatures. Plants prepare themselves during late summer and fall through a process called cold acclimation. As cooler temperatures prevail and the day length shortens the process of cold acclimation begins. This helps protects plants against winter injury. We all remember the extreme cold temperatures from last winter that caused much damage to many of our ornamentals.
Winterization can be interrupted as it has this year due to unseasonably warm temperatures in November. My red buckeye actually leafed out and blossomed. We also saw forsythia blooming as well. If cold weather is not long enough, plants think that winter is over and act accordingly. The problem is that old man winter usually comes roaring back as it did already.
Cold temperatures damage plants in several ways. Plant stems, fruit, leaves, trunks and roots can all be injured by the cold. Leaves and stems are the first places to look. As ice forms within the cells of the plant, the tissue dies and the stems and leaves turn mushy and brownish-black. Roots can also be damaged and not noticed until spring arrives and the plant fails to leaf out.
Windy conditions along with cold temperatures damages plants through desiccation. The wind scavenges moisture off the plant at a greater rate than is being absorbed so the plant dehydrates. This is why you should wrap or protect the foliage of new plants when transporting them in the back of a pickup. If you want to make your Christmas trees last longer, protect the needles from being desiccated.
We all know not to prune spring flowering ornamentals in the fall. Cold temperatures can do a pretty good job of it though. Check the flower and leaf buds after a cold snap. Cut them open and check the color. They should be green throughout, if brown or darkened, they have been damaged.
On woody ornamentals the bark may split and frost cankers appear. This may damage the cambium, which contains the xylem and phloem tissue, which in turn transports nutrients throughout the plant. Depending on where the damage occurs, bark splitting may also kill the plant.
Extremely cold temperatures can cause vertical cracks in the trunk of the tree. As the temperature of the trunk cools down quickly, the trunk contracts and splits. This is not common in Georgia.
The best way to prevent cold damage is to select plants adapted to our area. Troup County lies along the fall line. We are in a transitional zone from the coastal plain to the Piedmont. Georgia and the United States are divided into plant zones. Troup County falls in zone 8a. Unfortunately, many plants better adapted to warmer zones may survive in most years in our zone. When we have an unusually cold year many ornamentals from those zones further south may suffer in Troup County.
The location in your yard is also important. Ornamentals planted in the north to northwest portion or in low areas may be subject to cold damage. Keeping plants healthy and following proper cultural practices can also prevent cold damage. Fall fertilization and pruning stimulates growth, which is more prone to cold damage. Send in a soil test before applying any fertilizer.
Windbreaks such as evergreen plantings, buildings and fences, can also protect ornamentals. They block cold winds and the invasion of cold air masses into the area. The best location is usually on the northwest side of the planting.
Plants protected by canopies or shade are less susceptible to winter desiccation. The canopy prevents heat loss on the calm, clear nights. If you get plenty of notice of a cold front, you may cover your plants or bring the containerized ones indoors. Mulching will protect the roots. You can reduce heat loss from the containerized plants by pushing them together and covering them with sheets, burlap or blankets. You may have to build a frame to prevent damage to the plants. Make sure you remove the covering during the day.
Check the water needs of your plants prior to the cold snap. Moist soil absorbs more heat thereby keeping the roots warmer. Mulch will hold the moisture.
After a freeze, wait a few days and then check for damage. Check the buds and then do a scratch test on the stems. If the stem has any black or brown or the leaves are black or brown, damage has occurred. After all danger of further freezes has passed, prune out the dead wood to the living tissue. The living tissue will be green under the scratch test.
Many thanks to Robert Westerfield and Orville Lindstrom for providing the background information.
Brian Maddy is the ANR Agent for Troup County Extension. The Troup County Extension office is located at 114 Church Street, La-Grange, GA. 30240 (706) 883-1675. Monday – Friday/ 8:00 AM – 12 noon and from 1:00 – 5:00PM.