What Is Green Manure?
Green manure is a crop grown mainly to be cut down or incorporated into the soil while still green, rather than harvested for sale or food. It can protect bare soil, add organic matter, and, when legumes are properly inoculated, contribute nitrogen for later crops.
Green-manure crops are often cover crops used during an otherwise empty period, such as late fall through spring or between cash-crop plantings. Common choices include cereal rye, oats, buckwheat, crimson clover, field peas, cowpeas, and forage radish. Choose a species based on the season, your expected planting window, drainage, and whether you need nitrogen, weed suppression, erosion control, or easier soil cover.
Legume green manures such as peas, clovers, vetches, and cowpeas can form a partnership with compatible rhizobia bacteria in root nodules. If the right bacteria are absent, the crop may not fix much nitrogen. Use the inoculant recommended for that legume when needed, and verify nodulation by gently examining roots for firm, pinkish interiors during active growth.
Terminate the crop before it produces viable seed. For most home gardens, mowing, cutting at the soil surface, or using a hoe is practical; then leave the residue as mulch or incorporate it shallowly. Incorporating large amounts of fresh material shortly before planting can temporarily complicate seedbed preparation, so allow time for residue to begin decomposing.
Timing matters greatly. Oats and field peas are useful cool-season options in many northern areas because winter usually kills them, leaving manageable residue for spring. Buckwheat grows quickly in warm weather and is commonly cut at first bloom, before seed set. Winter-hardy rye and vetch need a deliberate spring termination plan several weeks before a direct-seeded crop.
A green manure is not a substitute for correcting every soil problem. Have soil tested through a Cooperative Extension-affiliated laboratory before relying on it to address low pH or nutrient deficiencies. Repeated cover cropping can improve tilth and reduce erosion, but compacted layers, poor drainage, and major nutrient imbalances may need separate management.
Avoid planting the same plant family repeatedly in the same space. For example, rotate brassica cover crops away from brassica vegetables when clubroot or other family-specific diseases are a concern. Also account for water use in dry regions: terminate a cover crop early enough that it does not exhaust moisture needed by the following crop.
Frequently asked questions
Is green manure the same as compost?
No. Compost is decomposed organic material applied to soil, while green manure is a living crop grown in place and then terminated.
Do I have to till green manure into the soil?
No. You can mow or cut it and leave it on the surface as mulch. Shallow incorporation is optional and depends on your planting system and residue amount.
How long should I wait after turning in green manure?
Allow roughly two to four weeks before direct seeding when substantial fresh residue was incorporated. Warm, moist soil speeds decomposition, while cool soil slows it.
General guidance for US home gardens. Conditions vary by region and season; check with your local Cooperative Extension office for site-specific advice. Page updated Aug 4, 2026.