By Crow Miller – It’s important to learn how to protect plants from frost because it just takes one night of freezing temperatures to spoil an autumn harvest you have been working and waiting for. And yet that first frost of fall is often followed by weeks of warm, sunny weather, a time for your garden to stay productive and enjoyable.
One simple way to prevent frost damage is to foliar spray all plants with a micro nutrient mix of fish/seaweed. This compensates for the stress of cold weather and makes plants frost resistant. This works well for light frosts, but for hard frosts, step two works best. Step two: Avert frost damage is to quick-freeze plants. Although it sounds almost like a complete contradiction, by using sprinkler irrigation, you can actually protect them from temperatures down as low as 20° to 25°F.
The secret behind the irrigation protection method is simply a principle of nature. When water changes to ice, it releases heat. A pound of water gives off 144-BTUs of heat in the freezing process. It is this latent or hidden heat that can be used to guard against sudden or unseasonable frosts. As water freezes on the plant, it creates a coating sometimes as much as a half-inch thick. Heat trapped underneath this protective coat is enough to keep fruits, vegetables, and flowers from a frostbitten end. Increased moisture in the air also serves as a blanket, reducing the amount of heat given off by crops through radiation. Safe from freezing, they emerge to finish ripening or colorfully bloom.
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The amount of frost protection possible through irrigation depends partly on wind conditions as well as temperature. On still, clear nights, many crops have been protected to 20°F. Turn on the sprinkler or irrigation systems when the temperature drops to 34°F.
Remember, ice on plants must be kept wet or melting at all times, continue irrigating until the air temperatures rises above 32°F, and all ice has melted off plants. The sun’s heat after daybreak will keep it melting following overnight frosts.
A crop that has been frosted may often be saved if the sprinkler is started before the temperature goes up; slower thawing lessens damage to plant tissues. Ice doesn’t always form when frost is very light, but it is a good idea to turn on the sprinkler before going to bed if the evening temperature drops to about 40°F and frost is likely in the forecast.
More conventional frost-stopping techniques are given wider application, too. Most growers have tried placing a row cover over favorite crops to protect it from freezing. Based on the principle of preventing loss of heat from the surface of the ground or from the plant itself, such covers generally keep temperatures higher than the outside air, often enough to prevent damage.
Extra Pointers for How to Protect Plants from Frost:
1.) Choose hardy, frost-resistant varieties whenever possible, especially for produce or flowers intended for early spring or fall growing.
2.) Watch the plant location. Frost settles into slopes or valleys above which is a belt of warmer air, a natural defense you can often capitalize on. Consider air movement and slope when selecting plant sites, particularly for sensitive or late season crops.
3.) Planting near water—consider this with your farm pond design or plant close to streams, rivers, and lakes—also helps, since these release heat on cold nights.
4.) Plant windbreaks where open stretches let winds gust through. Sheltered fields may be as much as 10°F warmer than exposed plots. Hedges, trees, walls, and fences serve the purpose. Cut openings in solid barriers so that air circulation is not hampered, creating frost pockets of still air.
5.) Don’t prune frost-damaged plants until after hard frosts are past and new growth starts below frozen parts. Nipped or blackened plants may look neater if cut but pruning at that time can result in greater damage from future freezes.
Finally, remember that fertile soils increase frost resistance. Remember this important soil fact: Plants winter better on soil properly cultivated and organically fed and balanced than on poor, badly tended soils. Learning how to compost at home to add nutrients to your soil is a great strategy for any gardener.
Originally published in the September/October 2008 issue of Countryside & Small Stock Journal and regularly vetted for accuracy.