Cover Crops and Green Manures for Gardens

A cover crop is a crop for the soil.

Green manures are plants you grow not to eat but to protect the ground between crops. They hold on to nutrients that winter rain would wash away, then give them back when you dig them in.

Updated 14 October 2026 · 5 sources

Cover the gaps
Mop up nutrients
Wait a month to plant
Green over winter, richer by spring

Pick a cover

THE SHORT ANSWER

Grow something
between the crops.

Bare soil loses what it holds.
A green cover keeps it.

WINTER

Catch the nutrients

The RHS says to sow green manures in late summer or autumn to mop up nutrients and stop winter rain washing them away. Dug in next spring, they give them back.

Pick a cover

WILDLIFE

Better than bare earth

Covered soil is much better for wildlife than bare ground. Phacelia flowers attract pollinators, and dense cover may draw in frogs and toads that eat slugs.

Choosing plants

DIGGING IN

Then give it a month

Chop the plants, dig them into the top 25 cm of soil and wait a month before sowing or planting: decaying green material can hold back new growth.

How to do it

A gardener's gloved hand driving a spade into a vegetable bed, turning chopped green leaves and stems into the dark soil — AI-generated image, not a photograph of a real person or place.

FOUR STEPS FOR A BARE BED

From bare bed
to green manure.

No fertiliser needed, and seed is cheap and easy to find. Here is the RHS method in four steps.

Sow thickly
Scatter the seed evenly over the bed and rake it in. Close sowing gives the cover you need to smother weeds.
Water until it takes
Keep seedlings watered in dry spells until they establish. After that, the cover looks after itself.
Chop before it gets tough
Cut it down and let it wilt. Chop or shred the foliage so it breaks down quickly in the soil.
Dig in, then wait
Work it into the top 25 cm of soil and wait a month before you sow or plant the next crop.

TWO NUMBERS WORTH KNOWING

Less nitrate lost,
more left for crops.

Two UK field trials on farms,
measuring what drains away under a cover.

75–88%

Cut in nitrate leaving field drains

In a Defra-funded Norfolk trial, an oilseed radish cover crop reduced nitrate leaching losses discharging into the river by 75% to 88%, and soil nitrate at 60–90 cm deep by 77%.

RIVER WENSUM TRIAL · UEA / DEFRA

up to 90%

Nitrate leaching, cover crop vs weedy stubble

Trials on farms in Hertfordshire and West Sussex found cover crop mixes cut nitrate leaching by up to 90% compared with weedy stubble, and added up to 35 kg of soil nitrogen per hectare the next spring.

NICCS PROJECT · ADAS

England's Sustainable Farming Incentive now pays farmers for multi-species winter cover crops, to protect the soil surface and minimise nutrient leaching, soil erosion and runoff.

A QUICK COVER CHECK

What kind of gap
do you have?

Pick the gap you need to fill. The value is a green manure the RHS suggests for it; the bar shows how long it typically stays in the ground.

Based on RHS advice on green manures. Sowing windows vary with region and weather.

Cover check

Choose your gapA few weeks in late summerOver winter, heavy soilOver winter, poor structureA no-dig bedResting a bed for a year or two

A few weeks in late summerMustard

Fast-growing mustard sown before mid-September can be dug in by October. It is a brassica, so do not follow it with cabbages: it can encourage clubroot.

Over winter, heavy soilWinter field bean

A hardy legume that is good for heavy soils. Sow from September to November and dig in up to flowering, two or three months later.

Over winter, poor structureGrazing rye

Good for soil structure and keeps growing all winter. Sow from August to November and dig it in the following spring.

A no-dig bedBristle oats

Sow in late summer. In spring, cover them with cardboard and the foliage composts where it lies, or cut it for the compost bin and leave the roots.

Resting a bed for a year or twoEssex red clover

A hardy perennial legume for loamy soils. Sow from March to August and leave it for a few months or up to one or two years.

Source: Royal Horticultural Society, Green manures (RHS Advice).

Lavender-blue phacelia flowers in full bloom across a garden bed, with a bee feeding on one of the curled flower heads — AI-generated image, not a photograph of a real person or place.

CHOOSING YOUR PLANTS

Mixtures beat
single species.

The RHS says mixtures are likely to be more effective than one plant alone. A homemade late-summer mix of bristle oats, crimson clover and phacelia works well.

Legumes such as clovers, vetches and field beans can fix nitrogen from the air, but only in summer. Brassica and legume covers belong in your crop rotation, as they share diseases with vegetables in the same families.

In conversation

Questions people ask

What is a green manure?

A green manure is a crop grown to benefit the soil rather than to eat. It covers bare ground between crops, protects the soil and returns nutrients when it is dug in.

When should I sow a green manure?

Most are sown in late summer or early autumn so they cover the soil over winter, then dug in the following spring. Fast summer covers such as mustard, phacelia and buckwheat fill shorter gaps.

Do clovers really add nitrogen?

Legumes such as clovers, vetches and field beans can fix nitrogen from the air in their root nodules, but the RHS notes they only do so in summer. Fenugreek is unlikely to fix nitrogen in the UK.

Are there any downsides?

Dense cover can shelter slugs and snails, brassica covers can encourage clubroot, and decaying plants can hold back new sowings, so wait a month after digging in.

Can I use green manures without digging?

Yes. The RHS suggests sowing bristle oats in late summer and covering them with cardboard in spring, so the foliage composts in place.

Sources

Each figure on this page comes from the sources below.

Never leave
soil bare.