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Cold Temperature Tolerance of Alfalfa
Seedling alfalfa is susceptible to cold temperatures from the time the seed (cotyledon) leaves emerge from the soil until four or five trifoliate (3-lobed) leaves develop on the main shoot.
Cold temperatures may destroy the tip of the alfalfa stem (growing point) causing the plant to be stunted, or the entire plant may wilt and die. Temperatures of 20 to 22 degrees are considered the threshold for killing alfalfa, although alfalfa may tolerate even colder temperatures. Alfalfa tolerance depends on factors such as variety, growth stage, plant moisture content, and length of time cold temperatures are present.
The decision of how to manage an alfalfa stand injured by cold spring temperatures is usually difficult. If new alfalfa growth has wilted or died, regrowth (which will be slow) must be initiated from live buds in the axils of lower stem leaves or the crown. Management guidelines for top growth damage that is severe includes grazing or mowing, and then delay harvest of regrowth until late bloom growth stage to maintain high stored food reserves. If one- third to one-half of the top growth has been wilted by frost and drying up, immediate mowing will permit earlier development of a new alfalfa crop. If alfalfa damage is light, harvest during the early bloom stage. The second harvest of all cold-injured alfalfa should be delayed to about the mid- bloom stage to allow recovery of stored food reserves.
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