Fall Alfalfa Harvest – When is it Wrong?

To give our alfalfa fields the best chance for persistence from one season to the next, we know they need to be healthy and rested as they head into winter, to best survive cold temperatures and ice damage.  We need to avoid sending them into winter in a tired condition where they’ve just used up a lot of root resources to regrow.  Current recommendations are to allow alfalfa stands to rest during a critical window prior to the first fall frost.  Alfalfa needs at least 900 GDD₄₁ to build sufficient root reserves to enter winter in good stead, or, if we give it less than 360 GDD₄₁ before the first frost, it will not deplete root reserves trying to regrow.  Between 360 and 900 GDD₄₁ is the window we want to avoid cutting alfalfa for best persistence.  For the bulk of the North Country, this window occurs between mid- to late-August and early- to mid-September.  For most of us, we’re within that ‘no alfalfa mowing’ window.  Refer to our September 2020 newsletter article for a list of this avoidance window calculated for 25 different North Country locations.