Developed by Dr. Mario A. Villarino, County Extension Agent for Agriculture and Natural Resources Hopkins County, Texas
We all know that freezes can kill plant tissues but do you know how? According to Texas A&M AgriLife Extension horticulturist, when the water inside a plant freezes it causes ice crystals to form that pierce the cell walls of the plant. When the temperature warms up, the cells leak out their fluids as they die and turn to mush. Freeze damage first shows up as dark, water-soaked tissues which then turn black to brown and dry up. Frosts on the other hand appear on the surface of plant tissues as well as on most any other exposed surface. During the night these surfaces radiate heat to the sky. When their temperature drops to the freezing point the water vapor next to it freezes on the surface. It is somewhat similar to the process on a warm day when water condenses on your iced tea glass because the glass is colder than the air around it. We can do a lot to protect plants from freeze because the temperatures are usually not too low and the duration is brief. Hopefully there is also not much wind, thus making protective measures easier and more effective. On the other hand when a hard freeze hits with a strong wind and lasts for a day or more there is usually little we can do to protect our gardens. The wind displaces any heat that might have helped protect the plants and speeds cooling of plant tissues. The extended time below freezing makes our simplest protective measures inadequate to the task. Sometimes all we need to do is keep a plant alive through the cold. 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. 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].