My cyber-sleuthing led me to a site for Sarah Bauder, Cooperative Extension forage field specialist with South Dakota State University. She wrote that winterkill and general stand loss of alfalfa caused great concern in many parts of South Dakota in recent years.
She observed that alfalfa winterkill most often is due to low, wet or flooded areas where plants were suffocated and died during winter. Most of South Dakota averages about 28 inches of annual precipitation – six inches fewer than what’s common in most of the Northeast.
Bauder wrote that if extreme winterkill hits an alfalfa field, plant stand evaluation should be performed. “If a field contains less than 39 stems per square foot, on average, stand replacement or modification should be considered. In newly seeded or young stands, we would expect more dense stands than in older, well-established alfalfa,” she wrote. “If a stand is mixed with grass, or in a very arid climate, lower stand counts are typically acceptable.”
She suggested one good way to assess an alfalfa stand’s survivability: count only stems that fit within a 19-inch-diameter ring that could be harvested by the mower. Exclude those under two inches tall. Use six to eight counts to create an average stem density estimate across the field. A 19-inch-diameter circle contains two square feet. Divide that count by two to get stems per square foot.
But Bauder cautioned that many farmers may wish to terminate thin, standing surviving alfalfa and quickly reseed with alfalfa. Studies share various rotation interval recommendations for reseeding alfalfa stands; the safest approach is to plant or interseed a different forage crop for the immediate season. Try to replant alfalfa the following spring. This allows time to reduce autotoxicity as well as soil-borne diseases and other pest issues.
Autotoxicity is essentially the same as allelopathy – “the phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival and reproduction of other organisms.”
My friend, retired career Extension agronomist and certified crop advisor Tom Kilcer, skillfully addressed the South Dakota research just mentioned. He wrote that in 2020 he and coworkers had conducted an experiment addressing winterkilled alfalfa. The original concept was that as soon as they determined that the stand was lost, growers could no-till red clover, or red clover and oats, to re-establish a forage legume for the next three years. Alfalfa allelopathy, a competition-repelling trait, had no effect on either crop.
Another alternative was to no-till just oats and harvest at boot stage in early June, then come back and no-till brown mid-rib sorghum or sorghum-sudangrass for a summer energy crop. It’s harvested in early September, then winter triticale is planted. The winter triticale is harvested for forage the following spring. Then alfalfa seed is no-tilled into the triticale stubble to reestablish the alfalfa forage crop.
Not too proud to admit failure, Kilcer wrote that in 2020, they tried the first part of planting oats followed by sorghum. The sorghum failed miserably, not growing at all. He believed that the oats had an allelopathic effect on sorghum, and strongly advised growers not to follow his example.
To determine if this was a weather fluke or a real issue, they repeated the study in 2021, adding another variable to the test. After harvesting the oats, in part of the oat plot they lightly tilled (one to two inches deep) with a disk to break up and incorporate the top inch or two of soil. Then they planted the sorghum-sudangrass. This time the crop behaved correctly.
He explained that where the sorghum was no-tilled into the oat stubble, that summer annual did not grow at all. But a lot of the still-living oats tillered and regrew. The sorghum in the lightly tilled ground, whether in fallow or oat stubble, grew very well with no oat allelopathy issues.

Alfalfa – good for livestock, preventing soil erosion, increasing soil nitrogen and carbon sequestration. Photo courtesy of Howard F. Schwartz, Colorado State, Bugwood.org
I recall vividly how parts of hay meadows that blow bare of snow can experience major winterkill of alfalfa, particularly clear-seeded stands. All that’s left is grasses volunteering in. The heaving action associated with the freezing/thawing stress yanks the plant out of the ground. Often the plant’s crown is snapped from its nodules, which remain imbedded in the soil. The result: dead alfalfa. I saw such an occurrence demonstrated most graphically during my field crops Extension career during the 1970s. At a research farm near Ithaca, a Cornell agronomy professor showed just how alfalfa winterkills.
Robert Seaney, Ph.D., showed how alfalfa heaves out of the soil if unprotected from the ravages of winter. He had signs posted next to the alfalfa “victims.” One sign read TON (toppled over – necrotic). Another sign read NVP (not very perky). In 2021, Seaney passed away at age 93. He was great crop scientist, and I count it a privilege to have known him. A Cornell Ag Life Sciences bulletin stated, “Seaney worked to identify the best forage species for the state’s soil and climate conditions. He also spent time developing forage management practices that would better support the high productivity of grazing cattle throughout the growing season. As part of his Extension programming, Seaney held tours and field days for cattle producers, crop growers and ag educators to learn more about specific techniques.”
Seaney discovered that “alfalfa is more likely to survive freeze-and-thaw heaving cycles when it’s mixed into a grassy hay stand instead of left standing on its own – thanks to the fibrous root networks that act like a shock absorber.” I never forgot that shock absorber analogy.
I also remember a Seaney lecture illustration that he used at a farmer meeting. He projected a slide on a screen in a classroom with crop growers. The slide featured a mixed mostly grass sod, with two or three alfalfa plants per square foot. He identified the photo as “a typical Southern Tier alfalfa stand.” After the audience stopped laughing, he explained how to avoid this disappointment on their own farms.
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