What is Green Manure?

Green manure is a term that encompasses several varieties of fast growing plants that are sown and then dug back into the soil to add nutrients and improve its structure.

When sown at the end of the summer, the plants can be left over winter and then dug in during the following spring. They will return goodness to the soil, replenishing the nutrients used up during the growing season while at the same time adding structurally important organic matter.

Another use for a green manure such as Mustard or Phacelia is during the summer when they can be grown and subsequently dug in between the harvesting of one crop and the next one being sown or planted.

There are several advantages of using green manure, especially in the vegetable garden. Over winter the plants will help to prevent bad weather eroding the soil and leaching nutrients, this is particularly valuable on sandy soils, and their foliage will discourage weed growth.

Green manure will initially absorb nutrients and, after digging in, these will be returned to the soil, Deep rooted plants such as Red Clover will bring nutrients nearer the surface so vegetables can benefit from them.

The soil's structure will also be enhanced by the addition of organic matter, improving its texture and drainage capabilities. One further advantage of sowing green manure is that some legume varieties such as Alfalfa and Fava Bean will fix nitrogen into the soil through bacteria in their roots.

Make sure the plant you use for green manure differs from the crop you have or are intending to grow. Prepare the soil as you would any other seed bed and then either sow seed into drills or broadcast over the plot.

Cut down before the crop flowers or begins to get woody and leave to wilt. Then dig in to a depth of about 6-10ins and leave for a fortnight before planting the subsequent crop.

Our recommendations for green manure plants:

  • Alfalfa*
  • Fava Bean*
  • Red Clover*
  • Mustard**
  • Phacelia**
  • Winter Tare*

* Fixes nitrogen **Between summer crops