Cover Crop Calculator
How much cover crop seed do you need? Published rates are lbs per acre — enter your bed size to get the pounds and ounces to buy.
Published broadcast rate: 100–120 lb/acre; the result uses the midpoint (110 lb/acre). Hand-sowing a garden bed counts as broadcast. Source: University of Missouri Extension — Cover Crops in Missouri (G4161).
You need
0.25lb seed
- Pounds
- 0.25 lb
- Ounces
- 4 oz
- Low–high range
- 3.7–4.4 oz (0.23–0.28 lb)
- Bed area
- 100 sq ft
- Method
- Broadcast
Planting window (Cereal (Winter) Rye): September to late October — ideally within 2 weeks of your area's 50% frost date. Can be planted later into winter in mild regions, but won't build much fall growth.
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Who needs a cover crop seed calculator
Cover crop seeding rates are published in pounds per acre, because that's how farmers buy and plant them — but almost no home garden bed is an acre. An acre is 43,560 sq ft, so a typical 4×8 raised bed (32 sq ft) needs less than 0.1% of an acre's seed. This calculator does that conversion for you: pick a crop and method, enter your bed size, and it scales the published rate down to the pounds and ounces you'll actually buy.
Every rate here comes from a state university extension — cited crop by crop below — not a guess. If you can't find a sourced rate for a crop you want to grow, that's a sign to check with your local extension office before guessing at how much to buy.
Cover crop seeding rates by crop
Rates vary by crop because seed size, germination rate, and how densely a crop needs to grow all differ. Legumes like clover and vetch are seeded much lighter than grasses like rye or wheat, which need a denser stand to out-compete weeds and build biomass. Use the broadcast rate when you're scattering by hand or with a spreader — that's nearly every garden bed. Use drilled only if a grain drill or seeder places the seed at a controlled depth.
| Crop | Drilled (lb/acre) | Broadcast (lb/acre) | Source |
|---|---|---|---|
| Cereal (winter) rye | 70–80 | 100–120 | Univ. of Missouri Extension |
| Crimson clover | 12–15 | 20 | Univ. of Missouri Extension |
| Hairy vetch | 15 | 20 | Univ. of Missouri Extension |
| Oats | 80–100 | 120–140 | Univ. of Missouri Extension |
| Winter wheat | 100–120 | 125–180 (drilled rate + 25–50%) | Penn State Extension |
| Field peas | 50–80 | 55–88 | Ohio State Extension |
| Buckwheat | 55–65 | 70–80 | Univ. of Missouri Extension |
Bottom line: broadcast always needs more seed than drilling the same crop, because scattered seed makes less reliable soil contact.
Converting lb/acre to a garden bed
The conversion is one division and one multiplication: divide the published rate by 43,560 (sq ft in an acre) to get lb per sq ft, then multiply by your bed's area. Cereal rye broadcast is 100–120 lb/acre, so the calculator uses the 110 lb/acre midpoint: 110 ÷ 43,560 ≈ 0.00253 lb/sq ft. For a 100 sq ft bed, that's about 0.25 lb, or 4.0 oz of seed (range 3.7–4.4 oz).
Small beds often work out to fractions of an ounce for lighter-seeded legumes, so don't be surprised by a tiny number — a kitchen scale or a measuring spoon (checked against the seed packet's weight) is usually more useful than a bag at that scale.
| Crop (broadcast rate) | 100 sq ft | 300 sq ft | 1,000 sq ft |
|---|---|---|---|
| Cereal rye (100–120 lb/acre) | 3.7–4.4 oz | 11.0–13.2 oz | 2.30–2.75 lb |
| Crimson clover (20 lb/acre) | 0.7 oz | 2.2 oz | 0.46 lb |
| Hairy vetch (20 lb/acre) | 0.7 oz | 2.2 oz | 0.46 lb |
| Oats (120–140 lb/acre) | 4.4–5.1 oz | 13.2–15.4 oz | 2.75–3.21 lb |
| Buckwheat (70–80 lb/acre) | 2.6–2.9 oz | 7.7–8.8 oz | 1.61–1.84 lb |
Bottom line: most home garden beds need only a few ounces of cover crop seed — buy the smallest packet size that covers your total.
Planting windows by crop
Timing matters as much as rate. Winter-hardy crops (rye, wheat, crimson clover, hairy vetch) need enough fall growth to establish roots before hard frost, but not so early that they bolt or get too tall to manage before winter. Oats and field peas can go in earlier and are often grown as a winterkill cover that dies back on its own, leaving a dead mulch. Buckwheat is the outlier — it's a summer crop, not a winter one, and dies at the first frost.
| Crop | Planting window |
|---|---|
| Cereal (winter) rye | September–late October |
| Crimson clover | 6–8 weeks before first frost |
| Hairy vetch | 30–45 days before first killing frost |
| Oats | Early July–mid-October |
| Winter wheat | Mid-August–late September |
| Field peas | Late March–April, or late July–September |
| Buckwheat | Mid-May–late August (summer only) |
How it's calculated
- 1
Pick a crop and method
Choose the cover crop and whether you'll broadcast it or drill it. Hand-sowing a garden bed is broadcasting, so that's the default. Broadcast rates are higher since more seed fails to make good soil contact.
- 2
Measure your bed
Enter length and width in feet, or type the total square footage directly.
- 3
Read your result
We take the middle of the crop's sourced lbs/acre range, divide by 43,560 to get lbs per sq ft, and multiply by your area. The low–high range shows under the result.
Frequently asked questions
How much cover crop seed do I need for a small garden bed?
Take the crop's lb/acre rate, divide by 43,560 (sq ft per acre), and multiply by your bed's square footage. A 100 sq ft bed of broadcast cereal rye at 100–120 lb/acre needs 3.7–4.4 oz of seed (4.0 oz at the midpoint) — this calculator does the math for your exact size.
Should I use the drilled or broadcast rate?
Use broadcast — the calculator's default — if you're scattering seed by hand or with a spreader, which covers almost every garden bed. It's a higher rate because more seed fails to reach good soil contact. Use drilled only if a grain drill or seeder places seed at a controlled depth.
Is buckwheat a winter cover crop?
No. Buckwheat is a fast-growing summer smother crop planted mid-May through late August; it's not winter-hardy and dies at the first frost. For a crop that overwinters, use cereal rye, winter wheat, crimson clover, or hairy vetch instead.
What if my crop isn't listed?
This calculator only includes crops with a seeding rate we could verify from a university extension, NRCS, or USDA source. If your crop isn't here, check with your local extension office for a sourced rate rather than guessing.