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FROST PROTECTION AND CONTROL

As well as the many other methods of aiding plants to survive in the north already mentioned, such as proper site selection and row covers, there are many other methods to help prevent early frost damage and extend the growing season. The first thing you should know is the temperature. That outdoor thermometer hanging by your window does not give you a clear picture of the temperature. The temperature that is used by the weatherman was obtained from a thermometer in a shelter at about 4 1/2' above the ground. But on calm nights, the minimum temperature at ground level is often 1.8 to 10.8°F (1 to 6°C) colder than this. This is significant because most frost damage occurs during clear calm nights.

After you have chosen your site and prepared it well, you can use another trick to help your plants. Site the plants in relation to their cold hardiness. Place the tender plants upslope where the danger of frost is the least. Avoid the low spots where the downflow of cold air might be hindered.

When frosts become imminent, managing the soil can provide an extended period free from frost. The idea is to use the heat stored in the soil to warm the air around the plants. This is readily achieved when the soil is bare, moist, packed, and not too rich in organic matter. All organic matter added late in the season prior to harvest should be well rotted and well worked in. Avoid loosening the soil which would lower the temperature of the soil surface by 1.8 to 5.4°F (1 to 3°C). Time tillage operations, hilling of plants etc. based on the weather reports. Packing loose soil, or watering it to consolidate it, will improve its heat retention and increase the availability of soil heat on cold nights. Weeds should be minimized and the use of ground covers and mulches avoided in the garden at this time. Note that this contradicts the procedure used in orchards but in this case we are trying to keep active growth going for a longer period of time.

Another way to extend the growing season is to use heaters or open fires to counteract the heat losses. A large number of small heaters is better than a few large ones. Needless to say, this method is for valuable crops only.

If crop shelters, as mentioned earlier for spring frost control, are used, often plants can be protected from the early frosts and another few weeks of growth can be accomplished.

Another method that has been tried, is using fans to mix the air near the ground with the warmer air above to moderate the temperature.

Sprinkling the plants with a fine mist of water will protect them down to 19°F (-7.2°C). The water should be applied at 1.2" per hour beginning when the temperature drops to 32°F (0°C) and turned off when the temperature returns to above freezing. The thin layer of ice that forms protects the plant by acting as insulation. It will often get the crops through the first few frosts and therefore extend the season, increase the yield and even double the yield in some instances.

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This page by Pat
updated August 18, 2000

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