What Is Green Manure?
Green manure is a crop grown mainly to protect and improve soil rather than to harvest for food. Its roots hold the ground together, while its leafy growth adds organic matter when cut down. It is especially useful on vacant vegetable beds through winter or between main crops.
Choose green manure according to the season and the gap in your cropping plan. For spring and summer, phacelia grows quickly and covers bare soil well. For autumn and winter, grazing rye, field beans, winter tares and clover are useful choices, depending on the bed and local conditions. Mustard can provide rapid cover in warmer months, but avoid using it where you are about to grow brassicas because it is from the same plant family. Read the seed packet for timing and suitability, as growth slows sharply in short winter days. In milder southern gardens, autumn sowings may establish later than in cooler northern areas or Scotland, where earlier sowing often gives better cover before cold weather.
Prepare the bed by removing old crops, perennial weeds and large roots. Rake the surface level, breaking only the largest clods, then water if conditions are very dry. Green manure does not require a beautifully fine seedbed; a reasonably even surface is enough. Scatter seed evenly, following the packet guidance, then rake lightly so seed has contact with soil. Firm the surface gently with the back of a rake or your hands. Protect newly sown beds from birds where necessary with fleece or netting held above the crop. Label the area clearly, especially on an allotment, so a helpful neighbour does not mistake the young crop for weeds and hoe it off.
Water seedlings during dry spells until they are established, then allow the green manure to grow with minimal interference. Check weekly for persistent perennial weeds and remove them before they become entangled in the crop. Green manure is not a cure for established weeds, so do not let couch grass, bindweed or docks hide beneath it. Dense leafy growth protects the soil from rain impact, reduces nutrient loss and gives soil organisms living roots to associate with. Flowering phacelia can also be attractive in a border or unused plot, but cut it before it sets seed if you do not want volunteers. Keep paths clear so you can inspect beds without treading on the soil.
Cut the crop before it flowers heavily, becomes woody or sets seed. Use secateurs, shears or a mower, leaving roots in the ground where they can decay and create channels. For soft growth, chop stems into short lengths and leave them on the surface as mulch for a week or two. Then either plant through the residue, or incorporate it lightly into the upper soil if you need a prepared seedbed. Do not bury a thick mass deeply, as it can decompose slowly and make planting awkward. Grazing rye is tougher than phacelia and needs cutting earlier and more finely. Allow several weeks between cutting a substantial crop and sowing small seeds, especially in cool spring weather.
Use green manure strategically between vegetable crops. Sow phacelia after early salads, spring onions or cleared broad beans, then cut it before planting autumn vegetables. Sow grazing rye or field beans after potatoes, courgettes or late summer crops, leaving them through winter and cutting in spring. Clover can suit longer-term pathways, orchard strips or beds resting for a season, because it is more persistent. Winter tares are useful where you want leafy cover and a later spring incorporation. Rotate plant families thoughtfully: avoid mustard before brassicas, and do not rely on one species year after year. A mixed sowing can give varied roots and cover, but use compatible species with similar sowing times.
After cutting, observe how the soil responds. You may notice fewer bare patches, more worms and a surface that is easier to work, but results depend on weather, soil type and how long the crop grew. Green manure does not replace mature garden compost, particularly on sandy soil that needs ongoing organic matter. Combine both practices: compost improves the bed directly, while green manure protects and roots it between crops. If slugs are a concern, clear dense cut material away from vulnerable young plants and check under cloches or fleece regularly. Keep notes on sowing dates, winter survival and the next crop's performance. Over several seasons, this helps you select the most useful green manure for your own garden.
Frequently asked questions
Do I need to dig green manure into the soil?
No. Cutting it and leaving the roots in place is often enough, especially if you use the chopped tops as surface mulch or add them to the compost heap. Light incorporation works for soft material when preparing a bed, but avoid burying large, woody amounts deeply. Letting it break down gradually is usually easier and kinder to soil structure.
Which green manure is best for winter?
Grazing rye, field beans and winter tares are dependable options for many UK gardens. Grazing rye is particularly hardy, while field beans and tares provide useful winter cover where they establish well. Sow early enough for your region, especially in cooler northern areas and Scotland, because plants make less growth once days become short and cold.
Can I sow green manure in a bed with weeds?
Remove perennial weeds first, as green manure will not eliminate them and may make their roots harder to reach. You can use a quick green manure after clearing annual weeds, provided seedlings have time to establish. Continue checking the bed and pull unwanted plants early, before they compete with or seed into the cover crop.
General guidance for UK home gardens and allotments. Conditions vary by region, soil and season; the RHS or a local garden centre can give site-specific advice. Page updated 19 Sep 2026.