When Should You Dig In Cover Crops?

Incorporating a cover crop at the right moment maximises its benefit and avoids problems. Too early and you sacrifice biomass and nitrogen that the crop is still building. Too late with a stemmy crop and incorporation becomes hard physical work and decomposition slows. The right timing differs between species and depends on what follows in the rotation.

The General Principle: Before Flowering or Stem Hardening

For most cover crops, the ideal incorporation point is before or at early flowering, when the plant has maximum nitrogen and nutrient content but its material is still soft enough to break down rapidly. Once stems become woody or fibrous — especially in grasses like winter rye — the carbon-to-nitrogen ratio rises sharply and decomposition slows. A stemmy incorporation will take six to eight weeks to break down fully rather than three to four.

Species-Specific Timing

Phacelia: Incorporate before flowers open, or in late winter if the frost has killed it. Dead frost-killed plants can be raked off or lightly incorporated from February onwards. Spring planting can follow two to three weeks after incorporation.

Mustard: Cut down before flowers set seed — typically eight to ten weeks after sowing. Incorporate immediately if using biofumigation benefit. Two weeks before planting is sufficient as material is soft.

Winter rye: Cut in late winter or early spring before stems become thick and hollow. Incorporate at least four weeks before any follow-on crop, and five to six weeks before direct sowing, due to allelopathic compounds in decomposing straw.

Field beans: Cut in late winter or early spring — February to April — before plants flower. Chop stems roughly before digging in. Allow four to six weeks before transplanting brassica seedlings.

Winter tares: Must be cut before flowering and seed set. In mild springs this can be March–April. Soft material breaks down in two to three weeks; planting can follow after three to four weeks.

Clover: Incorporate in spring before flowering begins. If left to flower and seed, clover becomes a weed. In a longer rest bed, clover can remain through a growing season, then be incorporated in late summer before autumn planting.

How to Actually Incorporate the Crop

For most cover crops, cut the top growth off at soil level first with a spade, shears, or strimmer. Then dig the chopped material in to about a spade's depth (20–25cm). You do not need to dig every scrap in perfectly — some surface material that gets mixed in will break down quickly. On no-dig beds, simply cut the material and leave it on the surface. It will break down as a surface mulch within three to eight weeks depending on species and temperature.

After Incorporation — the Waiting Period

Allow the following minimum gaps between incorporation and planting:

• Phacelia, mustard, winter tares: 2–3 weeks minimum
• Field beans, clover: 3–4 weeks minimum
• Winter rye: 4–6 weeks minimum (longer for direct sowing)