Frost can decimate your plants if you do not take precautions to protect them before it strikes. Naturally you should listen to the weather forecasts, but there are some signs that you can look out for to warn of impending freezing temperatures. These include keeping an eye on the sky, feeling the breeze and checking the moisture. This article by Eliot Tozer goes into more detail.

It’s late fall. The sky is blue, and the sun is bright. Then your local weather forecaster ruins everything with these chilling words: “Possible frost tonight.” Once the initial panic subsides, reason sets in. Frost is a local event, and it’s possible to predict with considerable certainty whether it will hit the plants in your garden. So relax, walk outside, and pay attention to these six signs to predict the likelihood of frost. Then, if necessary, spring into action.

1. Look Skyward

Clear, calm skies and falling afternoon temperatures are usually the perfect conditions for frost. Frost (also called white or hoarfrost) occurs when air temperatures dip below 32?F and ice crystals form on the plant leaves, injuring and sometimes killing tender plants. However, if temperatures are falling fast under clear, windy skies — especially when the wind is out of the northwest — it may indicate the approach of a mass of polar air and a hard freeze. A hard, or killing, frost is based on movements of large air masses. The result is below-freezing temperatures that generally kill all but the most cold-tolerant plants.
But if you see clouds in the sky — especially if they are lowering and thickening — you’re in luck. Here’s why. During the day, the sun’s radiant heat warms the earth. After sunset, the heat radiates upward, lowering temperatures near the ground. However, if the night is overcast, the clouds act like a blanket, trapping heat and keeping air temperatures warm enough to prevent frost.

2. Feel the Breeze

Wind also influences the likelihood of frost. In the absence of wind, the coldest air settles to the ground. The temperature at plant level may be freezing, even though at eye level it is above freezing. A gentle breeze, however, will prevent this settling, keep temperatures higher, and save your plants. Of course, if the wind is below freezing, you’ll probably have fried green tomatoes for tomorrow’s supper.

3. Check the Moisture

Just as clouds and gentle winds are your friends, so are humidity and moisture. When moisture condenses out of humid air, it releases heat. Not much heat, true, but perhaps enough to save the cleomes. If the air is dry, though, the moisture in the soil will evaporate. Evaporation requires heat, so this process removes warmth that could save your peppers.

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Image source: Susanne Nilsson