Green Manure Crops for Spring Soil Building

By Priya Sharma · October 8, 2026

What Green Manure Is

Green manure is a crop grown specifically to be cut and incorporated into soil while still green and succulent. Unlike cover crops (which may be left as mulch), green manures are tilled or chopped into the top few inches of soil where they decompose rapidly, releasing nutrients for the next crop.

Buckwheat: The Fast Grower

Buckwheat goes from seed to flower in 30-40 days, making it ideal for filling gaps between spring and fall crops. It suppresses weeds through rapid canopy closure, attracts beneficial insects with its flowers, and solubilizes phosphorus from soil minerals. Cut it before it sets seed to prevent volunteer plants.

Spring Field Peas

Field peas (Austrian winter peas or spring peas) fix nitrogen and produce succulent biomass that decomposes quickly. Sow in early spring as soon as soil can be worked. Cut and incorporate 6-8 weeks later, about 2 weeks before planting your main crop. They fix 60-100 lbs of nitrogen per acre.

Mustard: Biofumigation

Mustard green manure releases glucosinolates as it decomposes — natural compounds that suppress soil-borne diseases, nematodes, and weed seeds. This biofumigation effect makes mustard valuable before planting disease-sensitive crops like tomatoes and potatoes. Grow for 45-60 days, then chop and incorporate immediately.

Phacelia: Pollinator Magnet

Phacelia produces prolific purple flowers that attract bees and predatory insects. Its dense fibrous root system improves soil structure. Grow for 8-10 weeks, then cut at flowering for maximum biomass. It decomposes in 2-3 weeks, making it a fast green manure between spring and summer crops.

Incorporation Technique

Mow or cut green manure at flowering stage (peak nitrogen in tissues). Let it wilt for 1-2 days on the surface, then chop into the top 4-6 inches of soil with a hoe or shallow tiller. Wait 2-3 weeks before planting to allow initial decomposition. Watering speeds the breakdown process.