Alfalfa-killing freezes aren’t what they used to be. In fact, other than perhaps the far Northern reaches of the U.S., alfalfa is barely showing signs of frost damage, if at all. This is unusual given that the calendar has now flipped to November.

Even though a 24°F temperature hasn’t registered yet on most thermometers, Craig Sheaffer says it’s still safe to go ahead and cut, if the forage is needed. The University of Minnesota’s extension forage agronomist notes that there are not enough growing degree days or time left for substantial alfalfa regrowth that would drain carbohydrate root reserves. Sheaffer does recommend leaving at least a 6-inch stubble to help insulate plant crowns by catching snow.

If rainfall has been sparse this fall, the forage agronomist asserts that this will not make alfalfa plants more prone to winterkill. “Fall moisture deficits actually help increase winter survival compared to well-watered conditions,” Sheaffer notes. “Irrigation is not necessary, and the longer growing season is favorable for the dormancy reaction and accumulation of energy reserves, which should reduce the risk of winter injury.”

Residue concerns

Aside from the need for feed, some alfalfa producers don’t like harvesting the overwintered plant stems in the next year’s first cutting because it has the potential to reduce forage quality.

“Plants that are left in the fall will lose their leaves and by the spring only dead stems remain,” Sheaffer explains. “If normal winter conditions occur, these stems will be mostly lodged and not picked up at the first harvest. But in years without normal snowfall, the stems can still be standing in the spring.”

The long-tenured Gopher State forage expert describes a study that was done last spring in north central Minnesota where seven alfalfa fields were sampled to determine how overwintered fall stems affected spring forage quality. The spring forage regrowth was harvested, including the dead fall stems, and then samples were separated into brown (overwintered stems) and green (new growth) factions.

Table 1 shows the first-harvest forage quality of spring plants (spring whole plants without dead stems) and overwintered dead stems from the previous fall (fall stems) when alfalfa was harvested at bud stage. Sheaffer notes that the winter of 2023-2024 had less than normal snowfall, so a greater proportion of dead stems were still upright by spring.

Table 1. Effect of overwintered stems on the crude protein (CP), neutral detergent fiber (NDF), and fiber digestibility of bud stage spring-harvested alfalfa.

“Stems from the previous fall had significantly lower crude protein and fiber digestibility and higher neutral detergent fiber than the spring forage regrowth without stems,” Sheaffer reports. “Harvesting the combined spring forage with the fall stems reduced the overall spring forage quality. Dead stems compromised about 10% of the total spring biomass,” he adds.

In years with a significant amount of standing overwintered dead stems, Sheaffer suggests that farmers can boost the first-cut quality by mowing the dead stems in early spring before alfalfa regrowth.