t’s a tempting thought. Thicken up a thin alfalfa stand by simply interseeding new alfalfa into the existing crop. Unfortunately, it’s not the same as throwing a little grass seed into the bare spots in your lawn. And, according to University of Wisconsin forage researcher Mike Rankin, PhD, it probably won’t work.

“In recent years, some agronomists have touted the merits of using high rates of fungicide seed treatment to successfully interseed existing alfalfa stands,” shares Rankin. However, autotoxicity, competition and disease factors still are major concerns that hinder the potential success of this practice.”

Rankin cites a University of Missouri study that showed new seeding – even with fungicide and insecticide applied at planting – yielded only 30 percent survival within eight inches of old plants, and 75 percent survival at 8 to 16 inches from old plants. Maximum growth and yield occurred when old plants were 16 to 24 inches away from new seedlings.

The upshot, say Rankin: “Current recommendation stands. Except in the case of severe winterkill in which old stands are basically non-existent, the practice of interseeding alfalfa into alfalfa to thicken stands has rarely been successful.” To read a longer summary of Rankin’s comments, follow this link.