What is green manure, and which should you choose?

Kitchen gardens, vegetable patches or allotment plots are highly productive for most of the year, but there comes a time when you’re more likely to see bare patches of earth than vegetables. 

Green manures are fast-growing plants raised from seed that can be sown on unused ground to improve the health of your soil and give your crops a boost. They are also referred to as 'cover crops'.

Read more about how to improve your soil

Why grow green manure?

There are many reasons why it’s worth sowing green manures, or cover crops. The foliage of these plants forms a dense living blanket that helps prevent weeds from taking hold, while providing a place for beneficial insects to shelter – some have flowers that attract pollinating creatures.

If sown after a vegetable crop has been harvested, they will take up nutrients from the soil and prevent them being washed away by winter rain. 

Some green manure crops can be left as mulch over winter after the foliage is killed by frost, while others are hardier and can be dug into the ground while still green in spring – this will help to make the soil easy to cultivate and release nutrients that can be taken up by any vegetables you grow.

Green manure crops belonging to the pea and bean family, known as legumes, are able to absorb nitrogen from the air in their roots.

Find out how to make comfrey tea

Which green manure?

Forage pea

Forage peas have deep roots that help break up soil. They absorbs nitrogen from the air and suppress weeds. Sow forage peas in autumn and dig into the ground in spring.

Italian rye grass

Italian rye grass prevents nutrient loss from the soil. Sow in September and dig into the ground the following spring.

Fenugreek

Sow fenugreek in summer to suppress weeds.

Field beans/vetches

Field beans/vetches are nitrogen-absorbing legumes. Sow in autumn and dig into the soil in spring.

Crimson clover

Crimson clover attracts wildlife, improves the structure of the soil and helps to add nitrogen. Sow crimson clover from early spring to early autumn. Cut down and dig in before the flowers set seed.

How to sow and grow

Roughly dig bare soil and rake to a flat finish.

Either sow seeds in rows or scatter across the surface and rake in gently. Water well. Plants can then be left to grow.

The foliage of most green manures should be chopped down before the plants to start to flower – leave the stems to wilt on the surface then dig into the top 15cm of the soil.

After digging in, wait for two weeks before planting or sowing any vegetables as the rotting green manure crop can have an adverse effect on the edibles you plan to grow.

Find out how to make a compost heap

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