Fall rest period for alfalfa in Canada

Key Points The fall rest period (sometimes called “critical fall harvest period”) for alfalfa is 450 growing degree days, base 5°C — or approximately 6-weeks — before the average date of the first killing frost (-4°C for several hours), when alfalfa stops growing. Not cutting during this period allows alfalfa plants to grow and build up sufficient root reserves to survive the winter and grow more aggressively in the spring. When cut early in the period, the alfalfa will use the existing root reserves for regrowth, “emptying the tank.” Later in the period, the alfalfa uses photosynthesis to produce carbohydrates and stores them as root reserves, “refilling the tank.” Cutting in the middle of the fall rest period (3rd or 4th week), when root reserves will be depleted and there may not be time to replenish them, is usually higher risk than cutting at either the beginning or the end of the rest period. The fall rest period begins around August 15th in Northern Ontario, August 30th in ...