Early frost in the fall often puts an untimely end to the gardening season and late frost in the spring may do a lot of damage to the blossoms of strawberry and other fruit crops.
In the fall the first frost is often followed by several weeks of good weather. If the plants can be protected, the harvest of tomatoes, lima beans, peppers and other vegetables can be extended for quite awhile. The problem is to bring the plants through that first cold spell.
Many methods of saving plants from frost have been utilized for many years with varying degrees of success.
Plastics film, wind breaks, smudge pots, heat burners, wind machines, chemical foam and sprinkling with water are some of the methods that have been successfully.
For gardeners, sprinkling with water at night at probably the most practical and the most promising method of staying off a killing frost. One or two nights of continuous sprinkling when frost is likely may prolong the gardening season by two or three weeks.
How does it work? Heat is applied in one way or another to turn ice into water.Similarly, to turn water into ice, heat is taken away.
When a sprinkler is used for frost protection, water is almost continuously sprayed on the plants and the soil. Because the air temperature surrounding the plants drops below freezing, the water starts to freeze on the plants.
When the water freezes, it gives off heat, some of which goesinto the plant leaves, some out into the air and some into the soil. The heat absorbed by the plant is enough to keep the plant above its freezing temperature, except when the air temperature is very low (below 20 degrees F.) or when the heat is rapidly removed by a cold wind and evaporative cooling lowers the plant temperature.
Water must be sprayed on the plant continously - or at frequent repeat intervals such as would be applied by a rapidly rotating sprinkler - to provide enough heat to keep the plant from freezing. The sprinkler cannot be moved during frost - protection work.
Still, clear nights with low temperatures forecast usually indicate possible rediation frosts. A cold mass of air moves into the area behind a cold frost. Then, if the wind dies down toward evening or during the night and the sky becomes clear, heat is radiated from the plant and the soil to the colder outer atmosphere.
Windborne freezes are likely to be more severe and may last all night and all day. Protection from windborne freezes by spriklers is usually less than successful than at other times because the wind rapidly removes most of the heat given off by the freezing water. Also, the water distribution pattern of the sprinklers may be badly distorted so that many areas of the garden are not properly covered.