Because this event is coming so late in the spring, lots of gardens are already planted and vulnerable to a frost. A frost occurs when temperatures get down to 32ºF at ground level, and water starts to freeze on plant surfaces. If water within the plant cell, or between the plant cells freeze, it can cause serious plant tissue damage.
Frost this weekend is most likely to damage or kill the leaves of warm-season plants like beans, corn, cantaloupe, cucumbers, eggplant, okra, southern peas, peppers, potatoes, sweet corn, sweetpotatoes, squash, tomatoes, and watermelon. If it gets below 31 degrees, we call it a hard frost or freeze. Some cool-season crops can take that for a limited period of time. These include broccoli, cabbage, cauliflower, chard, English peas, lettuce, mustard, onion, radishes, and turnips. They will likely suffer leaf damage if it gets too cold, but typically survive.
If the temperature does go below 26ºF in a hard freeze, for any extended period, it will be the cold season crops like Brussels sprouts, beets, collards, kale, parsley, and spinach that make it through. But the worst case predictions I have heard have not been anywhere near that low.
Protecting gardens from these cold temperatures can be a challenge. But it can be done. One method that can help you get your plants through is to water your garden before the expected freezing temperatures. The wet soil will have more ability to hold heat, that will be helpful in getting the plants through the night and early morning. Don’t cultivate between now and the possible frost event. Cultivation actually can encourage loss of moisture from the soil which reduces the heat holding ability of the soil.
Another important method you should use is to trap heat in with the plants by draping the plant with a frost cloth or sheet. You might need to support this cover so that it floats over the plants, depending on how delicate they are. Cover all the way to the ground. Doing this will help trap heat and keep it from escaping from the soil to the surrounding air, while at the same time preventing heat from radiating away from the leaves into the atmosphere. Otherwise, on a clear, still night, as we expect this weekend, the temperature at the plant surfaces can drop below the air temperature measured above the plant as heat radiates from the plant by infrared radiation. Covering plants with a sheet or frost cloth will greatly reduce that radiation heat loss, while it also holds in heat from the soil.
I wish all you Lincoln County gardeners well as we face this strangely late possible frost. Hopefully, the predictions will prove to be incorrect, and we will have an uneventful garden weekend. But just in case, water the garden Saturday afternoon, tuck it in under some sheets, and hang on tight as we all hope for the best!
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