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Frost heave is the result of pressure created from a combination of freezing temperatures and soil defrosting. The fluctuating freezing and thawing conditions heave, or lift, the soil, which is often characterized by deep cracking of the soil. Plants may be uprooted from the ground as well. For many gardeners, this can become a major issue, as entire crops can be lost or damaged. Plants can quickly dry out and die once their roots have become exposed to cold temperatures. This heaving of the soil can also cause structural damage, in the form of cracks, on roadways, buildings and foundations. This damage can range from minor to major depending on location, weather conditions and soil structure.
While frost heave usually occurs in early spring, it can happen during late fall as well. This is when seasonal temperatures fluctuate most. Frost heaves are favorable whenever there is an abundance of cold air and soil moisture. Soil freezing results from this cold air, soil moisture combination. As it sinks to the ground, cold air causes water within the soil to freeze. Any additional moisture, such as that from soil defrosting, is drawn upward, freezing as well. When water freezes, it expands, creating pressure—both upward and downward. It is this pressure which causes frost heave to occur. Heaves are also more likely to happen in moisture-retaining soils such as loam, silt and clay. Well-draining soil, like that of coarse sand, rarely if ever suffers from frost heaving issues.
Although frost heave cannot be completely eradicated, as it is simply an act of nature, it can be prevented. Most heaving problems begin in low-lying areas of the landscape. Dips or depressions in the ground hold water. With the right soil and freezing temperatures, frost heave is inevitable. Therefore, it often helps to rake or smooth out these areas in order to minimize frost heaving threats. Soil moisture can also be alleviated by amending the soil with compost. Not only will this improve drainage issues, but it can also help with soil structure. Well-draining soil also warms up faster, further lessening the occurrence of frost heave. Another way to warm the soil is by applying mulch where suitable. Mulch helps insulate the soil by regulating temperature fluctuations and reducing frost penetration.