Frost Tolerance of Vegetables

Frost Tolerance of Vegetables

By Bob Randall, Updated January 2024

With our first frost and hard freeze of the year fore-casted for Mon, Jan15th through Tu, Jan16th, it is time for extra protection of tropical plants and harvesting all of your crops.

Usually, staring in early fall, it pays to keep an eye on nighttime temperatures so that you get your frost-sensitive crops harvested before the first frost.

What is frost tolerance?

Frost tolerance is a crop’s ability to survive a frost or below freezing temperatures. When air is cooled to below the dew point, dew can be formed on surfaces; if temperatures are also below 36°F, the result is frost, which is frozen ice crystals. A light freeze is considered 28°–32°F, and a hard freeze below 28°F.

Any temperature below 25°F is dangerous territory for most vegetable plants.

Why are some plants more frost tolerant than others?

Frost or freeze damage occurs when the water in plant cells expands as it turns to ice, and then bursts the cell walls. However, when the temperatures cool, cool season veggies and other cold-hardy varieties may produce more sugars, and sugar water freezes at a lower temperaturethan water, which keeps the water in the cells from freezing and bursting the cell walls.

This is also why frost-tolerant vegetables tend to get sweeter with cool temperatures. The sweetening process takes time, providing the most protection when the autumn cool-down is slow and consistent. Sweetening is one of a few strategies plants may have to avoid frost or freeze damage, and it is a strategy often seen in cool season vegetables. Shorter varieties have the advantage of being closer to the ground, which isinsulated and radiates some heat, often enough to quell the possible effects of short bursts of freezing temperatures. Also, the more mature the frost- tolerant plant, the better able it is to withstand frost or freezing.

Humidity can help protect plants from frost because moisture holds heat, effectively insulating the air. However, a clear or windy night can sweep away any warm air radiating from the ground, allowing colder air to sink in.

TIP: Water all of your plants and garden beds before temperatures drop below freezing.

Ways to Protect Annual Plants

https://youtu.be/crkcv75I2OA?si=f6n4Gbaj8SkdKFuf

Crop frost-tolerance varies between varieties. Greens like kale or spinach, and especially those with savoyed, wavy, curled, or textured leaves are generally hardier. Mulched root crops like beets, carrots, leeks, radishes, and parsnips can be harvested later in fall before the ground freezes, and some even survive a ground freeze. Search for your crops below to determine their frost tolerance level.

Likely damaged or killed by light frost <32˚F: All plants typically planted between March and August here.

Can withstand light frost>28˚F: artichokes, cauliflower, celery, bok choy and Napa cabbage, winter peas, radicchio, potatoes. Perhaps dill and fennel.

Can withstand hard frost: <25˚F for 2 hours+: arugula, broccoli, beets, carrots, endive, escarole, Tuscan kale, kohlrabi, lettuce, mustard, turnips

Can withstand bad freeze possibly with damage <22˚F: Cabbage, collards, garlic, leeks, parsley, bulb onions, multiplying onions, fava beans

Can withstand temperatures below 15˚F: Brussels sprouts, spinach, perhaps garlic.

 

Cover and weight down plants already up with hay and leaves. Add one or two buckets of water close to the base of the trunk. Then, tent and cover the whole tree or shrub and including buckets, with frost-cloth, tarp and or blankets. The buckets of water upon freezing, will release heat.

For garden beds, cover completely with frost-cloth or blankets to tent the garden bed, then weigh down the edges with bricks to keep the tent sealed and not blow away from wind.