Garden Tips Newsletter
What to do about cold damaged plants
January 19, 2009
I think the mild winters of the last several years have spoiled us. The cold temperatures we experienced last week were not really abnormally low for most areas. Where I live in north Mississippi we had a low one night of 7 degrees Fahrenheit. That is within the range of minimum temperatures for our Zone 7.
What was abnormal and potentially very damaging to plant material was the 30 to 40 degree drop in temperature in less than 24 hours that some areas experienced. Couple that with the high winds and you can get a wind chill effect and desiccation of some evergreen foliage.
Plants, to survive, must slowly acclimate or 'harden off' to withstand changes in their environment. A sudden change can severely shock a plant or kill it. That's why unknowing, but well-meaning people, can cook their houseplants when they move them outdoors into full sun in the spring. Or tender greenhouse-grown cabbage plants, when transplanted in the early spring garden, can be killed by sudden cold temperatures they would otherwise be tolerant of. These plants have not gone through a process of slowly changing to adjust to their environment.
I'm afraid that the sudden drop in temperature did some damage to trees, shrubs and 'evergreen' perennials. Some of my herbs that are evergreen such as thyme, sage, rosemary and oregano look absolutely horrible. Other herbs that can be evergreen in mild winters such as the mints and the Texas tarragon (Tagetes lucida) have been killed to the ground. In the southern part of the state, roses and other deciduous plants had already begun new growth that was damaged by the severe cold.
What to do? Short answer is nothing right now. If you have cold damaged plants don't prune or 'mess' with them in any way. Wait until closer to spring or even summer when the damage is easily visible to do any pruning. Here’s the good news. Plants are very resilient and most will recover, put on new growth in the spring, and do just fine.
Lelia Scott Kelly, Ph.D., writes Garden Tips weekly and is a Horticulture Specialist with the Mississippi State University Extension Service. Her office is in the North Mississippi Research & Extension Center, Verona.