History tells us our coldest weather comes to the Mid-South in late January and continues through early March. Here are some tips to help keep your tender plants safe.
Desiccation: The Wind Problem
When soil temperatures drop in winter, water absorption by the plant shuts down. With cold ground, brisk winds will dry the stems of many plants, especially those with green stems like gardenias, and cause some stem dieback. If it stays cold and windy long enough, the plant may be killed to the ground.
Fortunately, we are entering this cold spell with well-hydrated plants from the wet fall we have had. If you sprayed dormant oil on the foliage and stems in the fall, the plant would be sealed against water loss, protecting it further. Another application of dormant oil will help ensure the benefits last through the coldest part of winter.
Temperature: The Bigger Threat
This is more of a problem than wind. Every plant has a temperature at which the stems or trunk can be damaged by cold. It varies by plant variety and by the microenvironment the plant is in. Soil temperature, sunlight, duration of the cold, wind desiccation, and the age of the plant all affect the threshold at which a plant can be killed. The lower the temperature, the more plants are likely to be damaged. Very low temperature combined with drying wind can be the one-two knockout punch for some plants.
Memphis has long been referred to as too far north for most plants and too far south for everything else. We grow many plants that are at the edge of their range, whether by winter cold or summer heat. The ones to watch most closely this month are the ones from south of here.
What You Can Do
You can protect low plants from the wind by covering them with leaves or pine needles. Many of your neighbors have already bagged them for you and brought them to the street. Larger plants can be covered with cotton sheets for wind protection.
We have all seen plants wrapped in plastic like a piece of candy, tied at the top and bottom. If it is 8° outside, it is 8° inside that plastic bag at night, and probably 80° or higher on a sunny day when the air temperature is near freezing. If you use plastic, it needs to be open in the back or have a slot in the top to allow heat to escape when the sun comes out. The plant can be damaged more by the heat than the wind.
Larger plants that need temperature protection should be covered with a large tarp, placed over the plant and as much ground as possible. You will get a little heat from the soil, and you can add Christmas lights or a utility lamp for extra heat. Monitor daytime temperatures under the tarp during sunny days.
With falling temperatures, you can protect plants by icing them down with the sprinkler as the cold moves in, but use caution not to overdo it and break the limbs. Snow also helps protect plants.
What to Expect After
Winter damage can occur any time bitter cold weather settles in over the Mid-South. All we can do is take steps to reduce the damage and hope for the best. Beyond that, there is nothing to do but wait for spring and see how much actual damage is done, and to what. Until then, keep watering throughout the winter whenever the temperature climbs high enough, if Mother Nature does not do it for you.