A:   The date you take your last harvest of alfalfa affects its winter survival and next spring's vigor. Alfalfa needs about six weeks of uninterrupted growth in the fall to become fully winterized. This winterterizing generally begins about three weeks before the average date of first frost. Your last harvest can occur anytime before winterizing begins or after the winterizing period is over with little worry about affecting stand life. But, harvest during winterizing can be risky.

During early fall, alfalfa plants detect that the amount of sunlight each day is getting less. This tells them that winter is coming so they change their growth process to help them winterize. If you cut your alfalfa during this winterizing period, the plant begins to regrow. This reduces its ability to winterize as fully as it would if it hadn’t been cut. First and foremost is to make sure your alfalfa gets a chance to grow well for a lengthy period of time in late summer to build its root nutrient reserves. This means allow at least six weeks between your previous cutting and the cut that occurs during winterization. Second, thoughtfully select fields to be cut during winterization. Avoid old, thinning fields unless you plan to rotate that field to a different crop next year. Young, healthy alfalfa fields containing varieties with good winter survival ratings are most likely to perform well even after cutting during winterization. Lastly, consider waiting until mid-October after winterization is over or plants are nearly dormant. The stress of regrowth following an extra late cutting usually is very small.

By mid-October the growing season is pretty much complete. Many folks received some late season rain and some areas have had light frosts that left alfalfa plants pretty much unaffected. So, you might have a substantial, high quality alfalfa crop remaining in your field. Alfalfa that has had at least six weeks of regrowth in mid-October since the previous cutting will have developed adequate winterhardiness for all but the most severe winters. It also has begun to go dormant naturally because of shorter days and cooler temperatures. As a result, harvest will not reduce winter reserves, nor is it likely to jeopardize stand persistence.