Harvesting alfalfa after frost
Dan Undersander, Forage Agronomist, University of Wisconsin
Regarding questions about frost on alfalfa the following pieces of information should be kept in mind:
- Has the alfalfa has really frozen? – this requires 4 or more hours at 24 degrees or less. Often the top leaf tips are frozen but not the crown.
- Alfalfa does not accumulate any toxic compounds after frost, unlike sorghums. Therefore it can be cut immediately after frost or any time later.
- The major consideration is how much the alfalfa will regrow. Alfalfa must either be cut early enough in the fall to regrow and replenish root carbohydrates and proteins or so late that the alfalfa does not regrow or use any root carbohydrates if we want good winter survival and rapid greenup for good yield next.
It is important to remember that we do not need to wait for a killing frost to take the last cutting. We must only wait until it is so cool that little or no regrowth will occur.