Purdue News
Purdue News
"Many fruits are best stored at 30 to 32 degrees Fahrenheit, so a light frost should not be of concern," said B. Rosie Lerner, Purdue University Cooperative Extension Service consumer horticulturist. "A hard frost may cause leaves to fall quickly, which may decrease further development of sugar in the fruits. A hard freeze -- temperatures down to 28 or below -- can physically damage the fruit."
If a freeze is predicted, Lerner said, not much of a practical nature can be done to protect an entire fruit tree. If fruits are ripe, they can be picked and used or stored. If fruits are not ripe, she said, they won't mature substantially once they're removed from the tree.
"For the very enthusiastic gardener, blankets or other coverings could be applied over a dwarf tree or grape arbor," Lerner said, "but even that would only provide a couple of degrees of protection."
Flower beds are a little easier to cover, and the horticulturist said gardeners can cover their flower beds to protect susceptible annuals with a tent of cloth.
"The materials should be supported by stakes to keep the weight of the cloth from breaking flower stems," she advised. "Most perennial flowers will tolerate light frost without problem, but some tender annual flowers, such as petunias, may be affected."
Vegetable plants also vary in their susceptibility to cold temperatures. Lerner said tender crops, such as tomatoes, peppers, melons and okra, cannot withstand frost unless protected by some insulation. Cool-season crops, such as cabbage, broccoli, Brussels sprouts and kohlrabi, will tolerate frost, or even a light freeze. Other crops, such as beets, carrots, lettuce and potatoes, will stand a light frost. In cases of light frost, sometimes only the upper and outer foliage are damaged, and the plants can still continue production.
"Mulching is a good way to protect very small gardens," Lerner said. "Use several layers of newspaper, straw or chopped cornstalks. For those with large gardens, it may be more practical to protect only a few plants of each crop. Blankets, tarps, floating row covers, or other large materials can be placed over rows of vegetables to supply insulation."
Cloches, paper tents, hot caps and plastic walls of water are the more expensive approaches to frost protection, but are very effective, according to the specialist.
If frost is predicted and plant covering isn't feasible, Lerner suggests picking as much produce as possible. She said some crops can be further ripened indoors if they're not fully mature.
"Light isn't necessary to ripen tomatoes, so most green tomatoes can be ripened to full red indoors," she explained. "In fact, direct sun may promote decay of the fruit from excessive heating.
"Ripening is mostly affected by temperature -- the warmer the temperature, the faster the ripening. To store tomatoes for later use, wrap the fruit individually in newspaper and store at 55 degrees Fahrenheit. The fruits will gradually ripen in several weeks."
The following chart lists most commonly grown vegetables and their tolerance to frost:
| Tender | Semi-Hardy | Hardy |
| (damaged by light frost) | (tolerate light frost) | (tolerate hard frost) |
| Beans | Beets | Broccoli |
| Cucumber | Carrot | Brussels sprouts |
| Eggplants | Cauliflower | Cabbage |
| Muskmelon | Celery | Collards |
| New Zealand Spinach | Chard | Kale |
| Okra | Chinese Cabbage | Kohlrabi |
| Pepper | Endive | Mustard Greens |
| Pumpkin | Lettuce | Onion |
| Squash | Parsnip | Parsley |
| Sweet Corn | Potato | Peas |
| Sweet Potato | Salsify | Radish |
| Tomato | Spinach | |
| Watermelon | Turnip |
Source: B. Rosie Lerner, (765) 494-1311; e-mail,
Writer: Andrea McCann, (765) 494-8406; e-mail, mccann@aes.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu
