Lawns, Gardens & Trees


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Get Ready for Jack Frost!

Jack Frost is coming to destroy our gardens. Let's get prepared.

Frost-damaged cherry tomato
Frost-damaged cherry tomato.

Jack Frost is coming to destroy our gardens. We can’t stop him—he comes every year—but we can be prepared.

Frost kills garden plants by exploding their cells. When the water in a cell freezes, it expands and then bursts open the cell walls. It’s like putting a can of soda in the freezer. The liquid expands and the can bursts! Frost-damaged tissues will become water-soaked and mushy.

Which plants are most sensitive?

The most sensitive vegetables include tomato, pepper, cucumber, pumpkin and squash. These plants require protection.

Broccoli, cabbage, carrot and radish can tolerate light frosts and do not require protection. The cool temperatures of fall will actually improve the flavor of these vegetables.

The most sensitive flowers include geranium, impatiens, begonia, zinnia, portulaca and coleus. Hardier flowers include aster, cosmos, morning glory, marigold and petunia.

How do you protect your plants?

That’s easy. Pretend YOU are outside in the garden. What would you wrap around yourself to stay warm?

I would like a blanket and so would your plants. Some gardeners use a tarp—that’s better than nothing.

Consider using layers of protection. Just like people use layers of clothes to keep warm, garden plants benefit from layers of protection. Two blankets are better than one.

Our first frost is usually a light one (29–32°F). In this case, we can protect our sensitive plants with a blanket or tarp. This will provide a few degrees of protection, which is all we need.

What about a killing frost?

When a hard, killing frost (28°F or colder) is expected, nothing will save your sensitive plants. Run outside and harvest whatever you can. Blemish-free tomatoes with a pink blush can ripen off the vine. Apples on trees tolerate temperatures down to 25°F before suffering damage.

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Photo courtesy of University of Maryland Extension.

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