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First Fall Frosts Trigger Concerns for Gardeners

“Are my tomatoes going to survive?” “Will my pumpkins and winter squash be damaged by the cold temperatures”?  “Are my plums and apples safe from frost damage”?

These and other similar questions are all too familiar with the first threats of universal frosts across the region. Generally, tomatoes and peppers are the ones that will be most adversely affected, and should be covered with a protective cotton sheet, tarp, newspaper tents, or an old blanket. Fruit trees like plum and apple will have pretty much a built-in protection assuming they are still carrying a fully foliated canopy. The leaves will act as protectants from temperatures that might dip into the lower 30’s or upper 20’s for a short period overnight. That, along with the sugars present in these fruits, will offer protection from these initial frost events. Not for long, however! As the trees defoliate, and these events occur with greater frequency, with increasingly lower temperatures, damage potential increases, and the best efforts to protect tomatoes and peppers will become futile exercises. Best Bet: harvest everything that is mature to ripen indoors.

Many pumpkins are still green at this date. They will not “yellow-up” if the vine has been killed by the low temperatures. They will stay green and simply rot thereafter. Root crops like carrots will handle the fall frosts with no problems; cabbage and lettuce likewise, until the temperature goes below 28 degrees F. for an extended period.

Likely damaged by light frost: Beans, cucumbers, eggplants, muskmelon, New Zealand spinach, okra, peppers, pumpkins, summer squash, sweet corn, tomatoes, watermelon, amaranth, and winter squash (plants).

Can withstand light frost: Artichokes, beets, carrots, cauliflower, celery, chinese cabbage, endive, lettuce, parsnips, peas, swiss chard, escarole, arugula, bok choy, mache, and radicchio.

Can withstand hard frost: Broccoli, Brussels sprouts, cabbage, collards, kale, kohlrabi, mustard, onions, parsley, peas, radishes, spinach, turnips, leeks, and sorrel.

It is important to understand that temperature is not the only factor affecting survivorship of plants during a frost event. The further a plant or its parts are from the ground, the more likely it is to be damaged by frost. The ground is usually still warm in early fall and will radiate some warmth to plants that are close to the ground. Humidity can also help protect plants from frost. Humid air holds more heat and reduces the drying effects of frost. Air movement also has an influence on frost damage. When wind blows during cold nights, it sweeps away any warm air trapped near structures or the ground, eliminating their insulating capabilities.

Tender plants can be protected from a few light frosts with row covers or blankets. Mulched beets, carrots, leeks, onions, radishes, and parsnips can be harvested later in fall before the ground freezes. Light frost makes leafy greens and root vegetables sweeter, so it's worth leaving some of your kale and carrots in the ground until you're ready to use them.

Ron Smith, PhD, Extension Horticulturist

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