What is Fall Dormancy in Alfalfa Plants?

When growing alfalfa, it is important to understand the significance of fall dormancy. Fall dormancy is what allows alfalfa to grow tall in the fall of the year.

The height of alfalfa plants that were planted in the spring should be measured approximately 25 days after they are cut in the fall. Dormancy is then scored from one to 11. A higher score indicates less dormancy. The shorter the alfafa, the more dormant it is. Alfalfa growers should be looking for the tallest alfalfa possible or, in other words, they want their alfalfa to be as non-dormant as possible.

In order to survive the cold winter months, alfalfa acclimates at the end of the summer. This acclimation is due to less sunlight and cooler temperatures. The greater the fall dormancy, the less likely plants are to survive a cold winter. Less fall dormancy will mean alfalfa plants will grow more in the fall, recover faster in the spring and produce a higher yield the following year. The key to success, then, is to plant the least dormant type of alfalfa that will likely survive the winter months. When figuring out this equation, the region where the alfalfa will be grown is essential.

Since the mid-1970s, alfalfa breeders have worked hard to sever the relationship between fall dormancy and winter survival rates. Fortunately, there has been great success in this area. This is significant because states such as Minnesota and Wisconsin used to grow alfalfa plants with fall dormancy scores of one or two. Now they are able to grow plants that score four or five. This allows for a much higher yield.

Higher scoring alfalfa plants means late-fall cutting can take place—allowing for more alfalfa hay to be stored. If no harvest takes place, a higher score still has its benefits. Unharvested fall growth can insulate the crown of the plant against the cold. It also can hold snow more than a harvested field. This means that survival chances are increased, as well as the next year’s yield. In the end, farmers can look forward to a higher alfalfa yield when they do not have to worry so much about fall dormancy rates and winter survival.