It’s overdue by a week or more, but it looks like even southern Minnesota will get its first frost overnight or in the next few days. How should a northern gardener respond? Winter is coming, of course, but there are ways to stretch out the season, whether that means a few more harvests from the vegetable garden or longer blooms on your favorite flowers.
Frosts, Freezes and Hard Freezes
A couple of years ago, we did a post explaining the differences between a frost, a freeze and a hard freeze. Basically, a frost involves temperatures below 36 degrees for several hours. A freeze means temperatures are between 28 and 32 degrees for four or more hours and a hard freeze means temperatures below 28 degrees for several hours. The air temperature in one part of your garden may vary from the rest of it, based on whether it’s a high or low spot, so make adjustments accordingly.
A hard freeze signals the end of the vegetable and annual flower gardening season unless you have invested in cold frames, hoop houses, a greenhouse or other season extenders. (If a greenhouse is on your wish list, check out the how-to story in the November/December 2021 issue of Northern Gardener.)
First Frost Strategies
Assuming you want to continue to harvest some late-season vegetables or keep a few containers healthy for a bit longer, a simple covering may be all you need until we get to the hard freeze stage. Some root crops won’t be affected much by early frosts because they are underground and the flavor of some hardy greens, such as kale, actually improves with a bit of frost. Tender greens, such as lettuces, will need a cover or you can harvest them. Other tender vegetables—and many Minnesota gardens still have tomatoes or peppers ripening in them this year—should be harvested.
Most annual flowers, such as impatiens, coleus, zinnias, petunias and calibrachoas, will die in a freeze. Pansies, snapdragons, sweet alyssum and calendula can handle frost but not a hard freeze. Depending on how low the temperatures go, you can cover displays or pick the flowers for a beautiful bouquet indoors. Those lovely mum pots you bought for your front porch are best covered up if the temps are going below the mid-30s, just to make sure they stay healthy for Halloween.
Beyond the First Frost
Eventually, it will be November in Minnesota, and that means more freezes and hard freezes and the end of the gardening season for all but those who extend the season with hoop houses or greenhouses. (Book recommendation, if that’s something you’d like to try.) It’s time, then, to clean up those areas that require it (vegetable gardens, containers) and allow those that do not require it to stand for the winter. It’s a great time to buy a few houseplants or an amaryllis for the holidays.