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Many gardeners are calling regarding the frost warnings for the next few nights. They are particularly worried about their vegetable crops and perhaps their apples, grapes, and pears.
Many fruits are best stored at 30-32 degrees F, so a light frost should not be of concern. A hard frost may cause leaves to fall quickly, which may decrease the 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 there is not much of a practical nature that one can do to protect the entire tree. If fruit are ripe, they should be picked and either used or stored. If fruit are not ripe, they will not mature substantially once they are removed from the tree. For the very enthusiastic gardener, blankets or other coverings could be applied over a dwarf tree or grape arbor, but even that would only provide a couple of degrees of protection.
Vegetable plants vary in their susceptibility to cold temperatures. 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.
Mulching is a good way to protect very small gardens. 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. In cases of light frost, sometimes only the upper and outer foliage are damaged, and the plants can still continue production.
If plant covering is not feasible, pick as much produce as possible if frost is predicted. Some crops can be further ripened indoors if they are not fully mature. Most green tomatoes can be ripened to full red indoors. Light is not necessary to ripen tomatoes. In fact, direct sun may promote decay of the fruit due to 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 F. The fruits will gradually ripen in several weeks.
The following chart lists most commonly grown vegetables and indicates their tolerance to frost.
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Information listed is valid only for the state of Indiana.
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The Plant & Pest Diagnostic Laboratory at Purdue University.