Thickening Alfalfa Stands
Last spring was a tough time getting good new alfalfa stands established and some older stands are facing natural thinnning. Given new alfalfa fields can be expensive to establish, you may want to consider thickening your existing stand by interseeding it. Fields less than one year old often can be thickened and salvaged fairly easily. Older fields, though, are a different story.
Thickening Older Alfalfa Stands
Seeding alfalfa into older alfalfa stands to thicken them usually doesn’t work well due to autotoxicity, the build-up of diseases, and competition from existing plants. Most of the time it’s better to seed an entirely new field in a new location. Sometimes, though, older stands can be thickened successfully. The best candidates are fields that are irrigated and on sandy or coarse-textured soils that are very well-drained.
Begin by harvesting the existing alfalfa. If the stand was weedy, control the weeds with herbicides, even if it might injure the existing alfalfa plants. Then get a drill that can cut into untilled soil and place new seed about one-quarter of an inch deep. Usually a grain drill in good condition with a box for small seeds will do, but sometimes you might need a more rugged no-till drill.
Drill seed as soon after harvest as possible. Any delay increases the risk of weeds and competition causing a failure. As existing alfalfa regrows, harvest it again early to help open the canopy so new seedlings will get more sunlight.
Then watch for weeds. Several herbicides can control weeds without much injury to new alfalfa.