In early fall, it pays to keep an eye on nighttime temperatures. Don't caught off guard by frost. Make sure to get the last of your crops harvested in time. To help you, here's a simple list of common vegetables and their frost tolerance.
Light Frost - Temperatures 28-32 degrees F
Hard Frost - Temperatures below 28 degrees F.
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 stuctures 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. Regardless of the protection from frost, natural or man-made, any temperature below 25 degrees F is dangerous territory for vegetable plants.
Early fall is a great time to sow salad crops in a cold frame for harvest in late fall and early winter. Bok choy, lettuce, mesclun, kale, mustard, and spinach are a few good varieties to try.