Green manures

Martyn Cox

Why we should fill bare patches in our vegetable plots with nutritious green manures.

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 veggies. 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.

Why grow them?

There are many reasons why it’s worth sowing green manures. 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.

Which green manure?

Forage pea Deep roots help to break up soil. Absorbs nitrogen from the air and suppresses weeds. Sow in autumn and dig into the ground in spring.

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

Fenugreek Sow in summer to suppress weeds.

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

Crimson clover Attracts wildlife, improves the structure of the soil and helps to add nitrogen. Sow 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.
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