Critical Fall Harvest Period for Alfalfa

When deciding to cut your hay stands late in the season, it is especially important in the case of alfalfa to observe the "critical fall harvest period" also known as the "fall rest period." Adequate root reserves are necessary for winter survival and persistence, as well as vigorous spring growth and good first cut yields. All alfalfa stands require enough time to prepare for the over wintering period, especially seedling stands. Harvesting before the critical fall harvest period for alfalfa allows the plants enough time before the killing frost to re-grow and build sufficient root energy reserves for over wintering. Harvesting during this period will reduce winter hardiness and potentially reduce stand densities the following spring. If harvesting before this period is not an option for you, you may also wait until after the killing frost to harvest.

The critical fall harvest period for alfalfa is approximately the final 450 Growing Degree Days (or approximately six weeks depending on location) of the growing season before the first killing frost. The map below shows estimated deadlines for harvesting alfalfa. Harvesting after the dates listed and before the killing frost for each region increases the likelihood of winterkill.

If the decision is made to harvest during the critical period, the benefits of the additional forage harvested should be weighed against the potential for winterkill and early spring yield losses. Yield sacrificed by not harvesting during the critical fall harvest period is usually easily regained in first cut yield the following year.