August 8, 2008

Last spring many people had a tough time starting new alfalfa stands, and some older stands thinned out over the winter.

New alfalfa fields are expensive to establish. If thin stands can be thickened by interseeding, it's cheaper than starting over.Young fields less than one year old often can be thickened and salvaged fairly easily. Older fields, though, are a different story.

Seeding alfalfa into older alfalfa stands to thicken them usually doesn't work well due to autotoxicity, build up of diseases, and competition from existing plants. Usually it's better to seed an entirely new field, preferably in a new location. Sometimes, though, older stands can be thickened successfully. The best candidates are irrigated fields on well drained sandy or coarse-textured soils.

Begin by harvesting alfalfa that already is there. 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 only about 1/4 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 early again to help open the canopy so new seedlings get more sunlight. Also be very watchful for weeds. Several herbicides can control weeds without much injury to new alfalfa.

Bruce Anderson
Extension Forage Specialist