Cover Crop Seed Calculator

Why cover crops earn their keep

Cover crops protect bare soil, feed biology, and — for legumes — add nitrogen. This calculator uses broadcast rates in pounds per 1,000 square feet from extension guides. Winter rye at 3 lb / 1,000 sq ft needs 1.5 lb on 500 sq ft. Crimson clover at 0.75 lb / 1,000 needs 0.375 lb exact on 500 sq ft, which rounds up to 0.5 lb when you buy in quarter-pound steps. Drilled rates run about one-third lower; we show that as a reference while keeping broadcast as the default plan.

Choosing a species

Winter rye is the tough winter workhorse for northern beds. Crimson clover and hairy vetch fix nitrogen when inoculated and established. Buckwheat is a summer smother crop that flowers fast for beneficials. Oats die in hard freezes (useful as a winterkilled mulch). Field peas pair with grains in cool weather. Match species to season — buckwheat in July will not replace rye in November.

Broadcast technique

Rake a seedbed, broadcast half the seed walking one direction and half crosswise, then rake lightly or roll for seed-soil contact. Birds love small seed — a thin straw mulch or closer timing before rain helps. Do not bury tiny clover seed deep. Water if rain fails in the first week. On windy days, sow in the evening or weigh seed with a light rake-in so half your purchase does not drift onto the lawn. Keep a kitchen scale in the shed; guessing “a handful” is how clover beds come up patchy.

Termination and timing

Plan how you will kill the cover before cash crops: mow, crimp, till, or winterkill. Letting rye go too mature makes it harder to terminate and can tie up nitrogen as it decomposes. Allow a couple of weeks between termination and transplanting heavy feeders when residue is thick. Use the seed-starting calendar so cover crop windows do not collide with indoor starts. Write the termination date on the same printout as the seeding rate so spring panic does not leave a six-foot rye forest beside tomato cages.

Mixes and inoculation

Multi-species mixes are excellent but need clear rates — when you blend, split the area’s seed budget rather than pouring full rate of each (that overseeds). Inoculate legumes with the correct rhizobia strain the day you sow. Old inoculant in a hot shed is dead inoculant. Buy seed sized for your area from the calculator’s “buy” line so you are not left finishing a bed with birdseed from the pantry.

Common mistakes: buying “a pound of rye” for a tiny bed and broadcasting it like grass seed until it mats, skipping inoculation on clover, and letting buckwheat set hard seed that volunteers forever. Another: measuring garden beds in “about half the yard” without square feet — pace off length × width so the rate table means something. Store leftover seed cool and dry; rye keeps better than onion seed ever will. If weeds already own the bed, terminate them before you sow or the cover crop starts behind.

Frequently asked questions