Know Your Frosts!

by Camryn Gamble, Big Sky Watershed Corps Member

Winter is coming, and that means it’s getting frosty! But what’s the difference between a light frost and a hard frost?

A light frost occurs when air temperatures drop to or just below freezing (32°F) for a few hours. Tender plants can be killed, but hardy plants, such as mums, may not be damaged. The effects of light frost vary from plant to plant but can include browning or scorching effect on foliage, all the way to a complete stem collapse. Therefore, it’s usually a good idea to provide all your plants with some light frost protection, such as covering them or mulching. Raised beds also help to guard plants from frost.

A hard frost, also referred to as a freeze, is when temperatures drop below 28°F for at least four consecutive hours. Most plants cannot withstand a hard frost, but some of the effects can be repaired with the help of pruning.

For some hard frost protection, try these tips:

1) Cover your garden beds with sheets of plastic or tarps that trap warmth from the ground.

2) Fasten covers over the canopies of shrubs with clothespins or spring clips to add a measure of protection.

3) Leave a sprinkler running so that it dribbles water onto your most valuable plants. The water droplets release heat as they cool to help prevent freezing.

Hardy plants that can withstand a hard frost include carrots, garlic, kale, radishes, spinach, and turnips to name a few. These plants can hold out during a hard frost, but they won’t live all winter, especially in our region. Less hardy frost-tolerant plants include beets, celery, potatoes, herbs, and flowers such as sunflowers and coneflowers. 

So, when the weather channel predicts a light frost, make sure to run out and cover your plants.  When a hard frost or freeze is in the forecast, harvest what you can and leave the rest in Mother Nature’s hands.

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Camryn Gamble is a Big Sky Watershed Corps Member assisting the Flathead and Lake Conservation Districts in the 2023-2024 season.