In much of the state our winters are brief with lots of moderate to cool temperatures interrupted by a few killing freezes. If we can take steps to help our plants through those cold snaps we can cheat the hardiness zone a bit in the landscape and keep a vegetable garden going all winter long. There are a number of techniques we can use to help avoid freeze damage to our plants. Here are a few of the more common ones.
Watering: There are two ways that water can help protect plants. First of all plants under drought stress can be more susceptible to cold damage. By watering plants several days or more before cold weather threatens you can relieve stress if they are suffering from drought. Water is also a great “heat sink.” That is, it holds warmth and releases it slowly, more slowly than plant surfaces or air. Watering your plants right before a freeze creates a source of warmth that will slowly lose its heat over the course of a long cold evening.
Another method is to cover the plants. Covering plants is the simplest, most practical way to protect against a frost or freeze. Gardeners head out with sheets, blankets, plastic, rowcovers and anything else that they can get their hands on to wrap up plants for a cold night. Keep in mind however that a blanket doesn’t keep a plant warm, at least not to any significant degree. Blankets keep us warm because our bodies produce heat that the blanket helps hold in. If you wrap up the branches of a small tree or shrub with a blanket you aren’t doing it much good.
The main source of heat for a plant is the soil. On a cold night heat from the soil rises up around the plants. If you use a blanket to trap this heat within the plant’s canopy you can make a very significant difference on a cold night.
When I talk about trapping heat I don’t necessarily mean warm air, just air that is warmer than freezing. If you keep the temperature around plants from dropping below freezing you have accomplished your goal. Even cold soil is actually significantly warmer than freezing and thus a source of “heat” on a cold night.
To cover plants effectively, lay the cover over the plant and allow it to drape down to the soil on all sides. Then secure it with boards, bricks, rocks or soil to hold in the air. This is especially helpful in preventing a breeze from cooling things down faster. The next day, remove the covers to allow the sun to warm the soil surface a little and then replace the covers as the sun goes down. For more information on this or any other agricultural topic please contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected].