Cover Crop Seed Calculator

How this is calculated

⚠️ THE SEEDING RATE COMES FROM YOUR SEED BAG, NOT FROM THIS PAGE. Rates differ enormously between species - a fine clover and a cereal rye are nowhere near each other by weight, because seed size differs by an order of magnitude - and they differ again between suppliers, between mixes, and by what you are trying to achieve. Your bag, your supplier's catalogue and your extension service all carry the figure for what you actually bought. A calculator that assumed one would be badly wrong for most readers, so this one asks. RATE IS USUALLY QUOTED PER 1,000 SQUARE FEET OR PER ACRE, and confusing the two is a factor of 43.56. An acre is 43,560 square feet, so a rate of 2 lb per 1,000 sq ft is about 87 lb per acre. Both figures are shown here so you can check yours against whichever unit the bag uses - if the per-acre figure looks absurd, you have entered the wrong one. ⚠️ BROADCASTING NEEDS MORE SEED THAN DRILLING, and the increase is an input rather than a constant because it depends on how you sow and what happens next. Seed scattered on the surface has to contend with birds, with drying out before its roots reach moisture, and with simply landing where it cannot establish. Seed placed into the soil at a set depth does not. How much extra to allow depends on your soil, your weather and whether you rake, roll or cover afterwards - your supplier's guidance is the place to get it, and raking or rolling after broadcasting cuts the loss substantially. BUY WHOLE BAGS AND EXPECT LEFTOVER. Seed is sold in fixed sizes and you rarely need a round number of them. Leftover cover crop seed stores reasonably well in a cool dry place, so the offcut is not usually wasted - but germination does fall with age, so a bag kept for several seasons may need sowing more thickly, which is its own small arithmetic problem next year. SOWING DATE MATTERS AS MUCH AS RATE, and this tool says nothing about it. A cover crop needs enough growing time to establish before winter, and the window depends on your climate and the species. Sown too late it does not develop enough top growth or root to do the job you wanted; sown too early it may run to seed. Your extension service publishes windows for your area. TERMINATION IS PART OF THE PLAN, NOT AN AFTERTHOUGHT. Decide before sowing how the crop comes out - cut and drop, dug in, winter-killed, or mown. Some species are considerably harder to kill than others, and a cover crop that becomes a weed has cost you more than it gave.

Common questions

Why won't it tell me the seeding rate?

Because rates differ enormously and there is no honest single figure. Seed size varies by an order of magnitude between species - a fine clover and a cereal rye are nowhere near each other by weight for the same ground coverage - and rates differ again between suppliers, between mixes, and according to what you are trying to achieve, since a crop grown for nitrogen and one grown for biomass are sown differently. Your bag, your supplier's catalogue and your extension service all carry the figure for what you actually bought, and that is the only one that describes your seed.

My bag quotes a rate per acre. What do I do?

Divide by 43.56 to get the rate per 1,000 square feet, since an acre is 43,560 square feet. The tool also reports your rate back per acre, so you can check it against the bag directly - and that check is worth doing, because mixing the two units is a factor of 43.56 and produces a number so far out that it is usually obvious once you look. If the per-acre figure the tool shows looks absurd against your bag, you have entered the wrong one.

Why does broadcasting need more seed?

Because scattered seed sitting on the surface has to survive things that drilled seed does not. Birds take a share, some dries out before its roots reach moisture, and some simply lands where it cannot establish - on a clod, in a crack, on the path. Seed placed into the soil at a consistent depth avoids most of that. How much extra to allow depends on your soil, your weather and what you do afterwards, which is why it is an input; raking or rolling after broadcasting cuts the loss substantially and is worth the effort on anything but the smallest patch.

What do I do with the leftover?

Store it cool, dry and sealed, and it will keep reasonably to the following season. The thing to know is that germination falls with age rather than stopping suddenly, so a bag kept for a couple of seasons will still grow but a lower proportion of it will - which means sowing a little more thickly to get the same stand. That is a judgement rather than a calculation. Seed kept somewhere warm or damp deteriorates much faster, and a shed that gets hot in summer is not a good store.

When should I sow it?

That is a question for your extension service, and this tool deliberately says nothing about it. A cover crop needs enough growing time to establish before winter, and the window depends on your climate, your season and the species - sown too late it never develops enough top growth or root to do the job you wanted, and sown too early some species will run to seed, which creates a weed problem rather than solving one. The rate this tool works out is correct regardless of date; the date is the part that decides whether the crop actually works.

How do I get rid of it afterwards?

Decide that before you sow, because it is genuinely part of choosing the species. Some cover crops winter-kill and simply collapse, which makes them easy. Others need cutting, mowing, digging in or smothering, and a few are hard enough to kill that they become a weed problem in their own right. A cover crop you cannot remove has cost you more than it gave. Your supplier's description usually says how a species terminates, and it is worth reading that line before the one about how much nitrogen it fixes.

Does it matter if I sow it too thickly?

It can. A very thick stand competes with itself, produces thinner weaker plants, and in a wet season can hold enough moisture at the surface to encourage disease. It also costs more in seed for no gain. That said, erring slightly heavy on a broadcast sowing is normal practice and is what the broadcasting increase is for - the difference between a sensible margin and a genuinely excessive rate is large, and the bag's own figure keeps you inside it.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Cover Crop Seed Calculator at https://www.bfcbrilliance.com/tools/cover-crop-seed-calculator.

What I entered:
- Area to sow (sq ft): ___
- Seeding rate from your bag (lb / 1000 sq ft): ___
- Extra for broadcasting (%): ___
- Bag size (lb): ___
- Price per bag ($): ___

What it calculated:
- Seed you need: ___
- Bags to buy: ___
- Cost: ___
- Seed left over: ___
- The same rate per acre: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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