How to use Green Manures

  • Prepare the soil by removing weeds, digging over if it hasn't been recently cultivated and raking level into a fine seed bed.
  • Scatter seeds over the surface of the soil at the recommended rate per square metre for specific crops.
  • Make sure the seed is in firm contact with the soil by gently tapping over the surface with the back of a spade or rake. Water in well.
  • Bare patches should be covered within two to three weeks and plants will the most beneficial if they are left for the recommended time period before digging in.
  • If plants start to flower before this, cut off the tops and either leave as a mulch or remove for composting.
  • Mowing or strimming is an essential part of growing most green manures, it is very important in weed control, especially when the crop is young. Early mowing can make the difference between a well-established green manure and one which is persistently weedy. Cutting also helps promote lush vegetative growth and delays the crop going to seed. Without topping most crops will become woody and difficult to incorporate. Ideally it is best to remove cuttings as this encourages more nitrogen fixation in legumes.

Incorporating Green Manures

  • Incorporation of a green manure can be done by rotavating or digging in, before doing this it is generally best to cut the crop with a mower (which will chop up the cuttings) as this makes the job much easier. Leave the green manure to decompose in the soil for up to two to three weeks before growing vegetables.

Types of Green Manures and Uses

Long term green manures. Usually established for two or three years where considerable organic matter and fertility building is required. They are normally cut monthly during the summer period and mowings/ clippings allowed to remain on the surface as a mulch. Such green manures may be pure clover if nitrogen fixation is a priority or a grass/clover mixture if organic matter build up is also important.

Winter green manures are usually sown in the autumn and incorporated in the following spring. They can be a good way of fitting a fertility building crop into a rotation if they can utilise land that would otherwise be bare. They need to be established early enough to do any good; if harvest of the preceding summer crop is delayed they may be more difficult to establish to be of any benefit. They can be legumes e.g. vetch, but a major use for this class of crop is to minimise nitrogen leaching; when used for this purpose they are often called winter cover crops.

Summer green manures are usually legumes grown to provide a boost of nitrogen in mid rotation. They may be grown for a whole season from April to September or for a shorter period between two crops. These shorter-term green manures can include non-legumes such as mustard and phacelia.

Green manures may also be used in intercropping systems or undersowing – this a way of providing addition Nitrogen during a crops growing period, aiding weed control and helping to prevent soil erosion. It is mainly used in Brassica crops and is sown once the crop is well established and growing well.

Greenhouses and Polytunnels Offering warmer temperatures throughout the year it is possible to sow ‘summer' green manures at any time of year allowing for the crop to be established and benefiting the soil during times it may be left fallow.

Green Manure & Bio-fumigation – Caliente Mustards have been shown to be a good green manure and an equally good bio-fumigant when incorporated into the soil at the correct time. They offer control for the suppression of weeds, soil nematodes and a range of soil-borne diseases.