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Green manures are fast-growing, non-edible crops sown specifically to protect and enrich the soil in vegetable beds. Rather than leaving ground bare between harvests, these plants act as a living mulch that can suppress weeds, reduce nutrient leaching during winter rains and improve soil structure. Depending on the species chosen, they can either add nitrogen to the soil or simply provide organic matter (humus) to support future crops.
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Choosing the right green manure
Selecting a green manure depends on your soil type, the current season, and what you intend to plant next. It is often more effective to use a mixture of species rather than a single crop to achieve multiple benefits simultaneously.
By soil type and goal
- Heavy or clay soils: Winter field beans and winter tares are suitable as they can handle heavier ground. Field beans are particularly useful for breaking up compacted soil with their deep roots.
- Light or sandy soils: Crimson clover is well-suited to lighter soils. Bitter blue lupin is another option for sandy, acid soils.
- Alkaline soils: Trefoil is a hardy option for light, dry alkaline conditions.
- Nutrient-poor soils: Buckwheat is a strong choice for soils lacking nutrients, as it grows well in poor conditions and produces significant foliage.
By seasonal timing
Over-wintering crops: Sown in late summer or autumn, these protect the soil through winter. Examples include grazing rye, winter tares, and Italian ryegrass. These are typically dug in the following spring.
Summer cover crops: These are used to rest ground between crops during the growing season. Phacelia, buckwheat, and fenugreek are quick-germinating options that provide cover in spring and summer.
By nutrient contribution
Legumes (members of the pea and bean family) such as vetches, clovers, and field beans have the ability to fix nitrogen from the air into their root nodules, which increases soil fertility. Other crops, like mustard or grazing rye, do not fix nitrogen but are excellent for suppressing weeds and improving soil structure.
Integrating green manures into crop rotations
Green manures must be treated as part of your vegetable rotation to avoid disease build-up. Because they belong to the same botanical families as many vegetables, they can host the same pathogens.
- Brassica family: Mustard is a fast-growing green manure, but it should not be sown in beds where you plan to grow cabbages, kale, or broccoli, as it can encourage the build-up of clubroot.
- Legume family: Clovers, tares, and lupins should be rotated just as you would with peas or beans to prevent soil-borne diseases.
Sowing and establishing the crop
Most small-seeded green manures can be broadcast. Follow the seed packet for sowing depth and spacing: larger seeds such as field beans may need deeper individual planting. For a broadcast crop:
- Broadcast sowing: Scatter the seeds evenly across the soil surface.
- Raking: Lightly rake the seeds into the surface to ensure good seed-to-soil contact.
- Watering: While fertilisers are generally unnecessary in late summer, watering is essential during dry periods until the seedlings are established.
For a head start, you can sow green manures in August between maturing crops, such as sweet corn, to ensure they are established before the weather cools.
Clearing and incorporating the crop
The timing of clearing is critical. To ensure the fastest decomposition and the retention of nutrients, green manures should be cut down before they flower, while the stems and leaves are still soft.
Traditional digging-in method
- Chop and wilt: Chop the foliage down to ground level and leave it to wilt. You may need to shred the material further if the growth is dense.
- Incorporate: Dig the plants and foliage into the upper soil, following the instructions for the chosen green manure and allowing for soil conditions. Persistent species may regrow and need further clearance.
- Wait: Allow at least one month between digging in the green manure and sowing your next crop. Decaying organic matter can hamper the growth of new seedlings if planted too soon.
No-dig clearing methods
If you follow a no-dig regime, you can avoid turning the soil entirely:
- Composting in situ: For crops like bristle oats, you can cut the foliage and cover it with cardboard in spring, allowing it to compost on the surface.
- Surface mulch: Cut the foliage and leave it on the soil surface to rot, or remove the top growth to add to a compost bin, leaving the roots in the ground to decompose and improve aeration.
Potential challenges and diagnosis
While beneficial, green manures can introduce specific issues that require management:
- Pest increase: The dense foliage created by green manures provides an ideal habitat for slugs and snails. Be prepared to implement pest control measures when you plant your primary vegetable crops.
- Growth suppression: If you notice your new seedlings are struggling or yellowing shortly after planting into a cleared bed, it may be because the green manure has not fully decomposed. Yellowing has other possible causes, so check soil moisture, root condition and timing rather than assuming decomposition is the cause.
- Weed competition: If the green manure is sown too sparsely, weeds may still penetrate the cover. Ensure a dense broadcast sow for maximum suppression.
Useful products for this job
The links below open Amazon UK product searches. Check the exact item, seller, current price and compatibility before buying.
- Garden rake: Necessary for raking broadcast-sown green manure seeds into the soil surface. Ensure the tines are suitable for light surface work rather than heavy debris removal. Search Amazon for Garden rake.
- Garden fork: Useful for the digging-in method when incorporating a suitable green manure into workable soil. Check for a sturdy handle and tines that can penetrate compacted clay soils. Search Amazon for Garden fork.
Related garden guides
Sources and further guidance
Guidance researched in September 2026. The feature image is an AI-generated illustration. Product guidance is based on published information, not hands-on testing.