Checked the weather lately? If so, then you know a hard freeze is in the forecast for Monday morning. The question is, Should you be worried?
The answer is, no. Freezes, even hard freezes this time of year are no big deal, at least so far as the vast majority of landscape plants are concerned -- more on that in a moment. But first, what’s the difference between a frost and a freeze, and which plants are most affected? Glad you asked.

Frost forms as a layer of ice crystals on plant surfaces, and can actually occur when temperatures are between 32 and 42 degrees, depending on the dew point. Frost most often forms at or near ground level, and when it lasts longer than a few hours, it can cause the water inside plants to freeze, which can lead to cell and tissue damage in tender plants.

A freeze occurs when temperatures are at or below 32 degrees, often several feet above ground level. A light freeze ranges between 29 and 32 degrees, and can cause even more damage depending on how long it lasts.

A hard freeze occurs when temperatures drop to or below 28 degrees for at least four hours. In some circles it’s also known as a killing freeze, especially when temps fall below 25 degrees. Regardless of what you call it, a hard freeze can kill certain plants. 

Spring frosts can cause light damage, whereas spring freezes can be downright deadly, and with any luck I won’t have to warn you about a late spring freeze. But since it’s fall after all, here’s what you need to know now. And why you can relax. Or chill.

Warm-season vegetables -- tomatoes and peppers, beans and cukes, for example -- won’t survive a fall frost or light freeze without protection, but cool-season veggies -- lettuce and other greens, broccoli, cabbage, cauliflower -- will, and their flavors will be improved because the colder temps cause the plants to concentrate sugars. Tender herbs such as basil and dill won’t survive either, but most culinary herbs are perennial and will be fine.

Tender annuals may bite the dust when covered in frost or subjected to freezing temps, especially Begonias, Calibrachoas (Million Bells), Coleus, Geraniums, Impatiens, Lantana, Marigolds, Petunias, and Zinnias. But microclimates may exist where temperatures stay well above 32 degrees, thereby enabling some of them to survive a while longer. Hardy annuals will fare better, but even they can’t survive a hard freeze. However, keep in mind that mums and pansies won’t be bothered.

Tropicals and houseplants (most of which are tropical), can’t handle frosts or freezes either, so if you haven’t already moved them indoors, do so now.

Trees, shrubs, and perennials actually began preparing for winter several weeks ago as daylight hours started to decline by making physiological changes that enable them to survive freezes. Back in late August, they began to slow their growth and concentrate sugars to begin the process of dormancy, which they’ll continue to do in the weeks ahead. In other words, they’ll be ready for winter.