Green manures & winter cover crops
Bare soil over winter is a wasted opportunity — and worse, our endless winter rain washes the goodness straight out of it. A green manure is the gardener's answer: a fast crop you grow not to eat, but to protect and feed the soil for free.
Sow it over an empty bed in late summer or autumn, let it blanket the ground through the cold, then dig it in — or simply cut it down — come spring. It's one of the kindest, cheapest things you can do for next year's harvest.
What a green manure does
- Protects the soil — a living cover stops winter rain compacting bare earth and washing nutrients away.
- Smothers weeds — a thick blanket of green leaves nowhere for weeds to get a foothold.
- Feeds the ground — dug in or left to rot, it adds organic matter; beans and clovers also fix nitrogen from the air.
- Holds the structure — roots keep the soil open and alive, and feed the worms and microbes that do the real work.
The best green manures for winter
For overwintering, the hardy ones are what you want — rye, field beans and tares stand up to the cold. The half-hardy ones (phacelia, clover, mustard) are best sown earlier, while there's still warmth to get them going.
Grazing rye
Very hardyThe hardiest of all. Masses of organic matter, superb weed suppression, and roots that hold the soil and its nutrients through winter rain.
Field beans (winter)
Very hardyA hardy bean that fixes nitrogen from the air into the soil — leaving the ground richer for next year's hungry, leafy crops.
Winter tares (vetch)
HardyAnother nitrogen-fixer with plenty of leafy bulk. Loves heavier soils and smothers weeds well.
Phacelia
Half-hardyFast, pretty and brilliant for bees if you let some flower. Half-hardy, so it may not survive a hard winter — best for milder spots or early sowing.
Crimson clover
Half-hardyA nitrogen-fixing clover with gorgeous red flowers for the pollinators. Half-hardy — sow early enough to establish before the cold.
Mustard
Half-hardyThe fastest of all and a natural soil cleanser (a 'biofumigant'). Frost-tender, so it dies back in winter — but it's a brassica, so don't use it where brassicas will follow.
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Putting a bed to bed
You don't sow green manure in neat rows — you broadcast it to cover the whole bed. Scatter the seed evenly, rake it in lightly, and water if it's dry. A classic, robust winter mix is grazing rye for bulk and weed-suppression with field beans for nitrogen, so the bed wakes up in spring richer than you left it.
A winter green-manure mix
Broadcast across the whole bed for full ground cover — here a hardy mix of grazing rye (bulk & weed suppression) and field beans (nitrogen). Rake in, and let it blanket the soil till spring.
How to sow it
- 1. Clear the bed of the spent crop and any big weeds, and rake the surface roughly level.
- 2. Scatter the seed evenly by hand across the whole bed — aim for a generous, even sprinkle rather than bare patches.
- 3. Rake it in lightly so most seed is just covered, and water if the soil is dry. Birds love the bigger seeds, so net field beans if they go missing.
- 4. Leave it to grow and do its quiet work all winter. In spring, dig it in or cut it down a few weeks before you want to plant.
One thing to watch: mustard is a brassica, so don't sow it where cabbages, kale or other brassicas will follow — keep it out of that part of your crop rotation.
Common questions
What is a green manure?
A green manure (or cover crop) is a fast-growing plant you sow to cover bare soil rather than to eat. It protects the ground from winter rain, suppresses weeds, and is dug in or cut down later to add organic matter and — with beans and clovers — nitrogen, feeding the soil for free.
What's the best green manure to sow in autumn?
Grazing rye is the toughest and best for bulk and weed suppression, while field beans and winter tares add nitrogen — sow these from late summer into autumn. Phacelia, clover and mustard are less hardy, so sow them earlier.
Do you have to dig green manure in?
No. The traditional way is to dig it into the top few inches a few weeks before sowing. But for no-dig, cut it down at the surface and leave it as a mulch (or compost it), and let the worms take the goodness down for you.