If you harvested first cut alfalfa and alfalfa-grass in mid-June you may be harvesting a third cut in late August. This assumes a 35-day interval between first and second cut, and 35-40 days between second and third. (Assuming 35- and 40-day intervals respectively, June 15th first cut = August 29th third cut.) This will in most cases preclude a fourth cut, though hope springs eternal. If we have adequate moisture and some warm weather your fourth crop may be looking pretty good by late September, but before heading out with the mower consider the following:
• Late-season alfalfa often looks a lot better than it yields because big leaflets are deceiving. If you decide to take a fall cut, either do the mowing yourself or be out there in the field when mowing starts in case you want to call a halt to the proceedings because of unexpectedly low yield.
• Autumn alfalfa-grass yield depends to some extent on the grass species you seeded with your alfalfa. Reed canarygrass doesn’t like fall weather, and as the nights turn chilly it goes dormant and turns a sickly orange. Tall fescue, on the other hand, does very well under fall growing conditions. One fall about 10 years ago when walking through one of the pastures at Miner Institute that we’d seeded with a pasture mix that included tall fescue I was amazed at the amount of this species: Lush forage, likely to be low in fiber and high in digestibility.
• Make sure there’s at least 45 days of alfalfa regrowth preceding any fall harvest unless it’s the last one before rotating to another crop. That’s to allow plenty of carbohydrate storage prior to winter. Even so, research has shown that first cut alfalfa yields the following spring are slightly to moderately lower following a fall harvest, a case of “Robbing Peter to pay Paul.”
• If you take a fall harvest, be sure to use a bacterial silage inoculant. (Only the foolhardy would attempt to make alfalfa hay in the fall.) The later in the fall you harvest, the more important a silage inoculant becomes. That’s because the population of “wild” fermentation bacteria declines with frost and extended cool temperatures. I think that inoculants are almost always worth the money but especially late in the season, when Mother Nature often needs a bit of an assist.