Whenever temperatures plummet during the winter, concerns rise about the health of alfalfa fields.
According to Dr. Dan Undersander, that concern is legitimate. In a document released on Jan. 9 after a stretch of bitterly cold temperatures, the University of Wisconsin Extension forage agronomist said, certainly, an alfalfa plant will die if exposed to cold enough temperatures.
However, the data indicates Wisconsin’s recent breathtakingly-cold spell will cause little to no injury or death of alfalfa.
Undersander explained that alfalfa generally survives winter and its periodic cold spells because it is hardy to temperatures of 10 to 15 degrees F. “This is the temperature of the crown, not the top growth,” he noted.
In addition, as little as four inches of loose snow will insulate the crown against up to 16 degrees F of air temperature. The crown is also insulated by the soil. Therefore, Undersander said, the critical temperature reading is two to four inches below the soil surface.
On Jan. 8, after the cold spell, the soil temperature of bare ground at four inches was in the single digits above 0 degrees F for all of the Midwest. The temperature was higher than the air temperature because of the insulating ability of the soil, Undersander noted.
However, soil temperatures at two to four inches under four or more inches of snow were generally 28 to 30 degrees F, he said. That’s well above the temperatures likely to cause injury to alfalfa.