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Winter damage to alfalfa plants varies, but many alfalfa fields will see relatively good plant survival, even following periods of severe cold temperatures. Horse owners who harvest alfalfa hay from their own land will want to check plants in early spring to find out if reseeding or renovation is necessary.

Alfalfa generally survives well during short spells of very low air temperatures. Though the leafy foliage may be frozen, the plant’s crown (tissue mass at ground level) is the crucial part that must stay viable for regrowth in the spring. While the air above a field may get very cold, the crown is insulated by the soil around it and also by layers of snow that help the plant stay at a temperature that may be well above that of the air. Damage usually occurs only during long periods of intense cold when the low temperatures penetrate two to four inches below the ground surface.

Some plants will be more susceptible to cold-weather damage because of disease. Plants that were mowed after dormancy in the fall are also at risk because they will not have had a chance to build carbohydrate stores in their roots before winter set in. In either case, these plants will not have enough energy for vigorous spring growth.

Guidelines developed by Iowa State University can be used to determine whether alfalfa fields are healthy, marginal, or in need of reseeding after a hard winter. Land owners should sample multiple areas of the field, measuring square-foot plots and counting alfalfa plants within each plot. When plants are dug up and split with a knife, healthy plants will show a creamy-white color in the center of the crown. Weak or diseased plants will have brown or yellow cores. In a field seeded two years previously, each square-foot plot should have at least five or six healthy plants. If more than half the plants have crown or root rot, reseeding is probably a good idea. Hay producers can check with the local agricultural extension office for more information on alfalfa viability.

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