Green Manures

By Jack Cox

In nature, soils are protected by a covering of grasses and weeds, which at the end of their growing cycle rot down and return their goodness to the soil. This is also the principle of ‘green manuring'; where a crop is grown for the sole purpose of returning it to the soil. 

By covering the ground with suitable plants you are helping to prevent the soil nutrients from being washed away by rain; as well as supplying a source of organic material to be returned eventually to the soil. In addition you are providing a form of weed control, 

A wide range of plants may be used for this purpose, even most annual weeds.

The important thing is to pull up the plants while still young, certainly well before they set seed, and let them rot down on the surface as a mulch. Or, if you prefer, you can dig them in. 

Plants need nitrogen in order to rot down. So rather than let the rotting plants take nitrogen from your soil, cut them while they still contain enough nutrients of their own to complete the process, and contribute to your soil fertility too!

So having discussed the basic principles, let us look at some of the more widely used green manure plants.

BEANS. All legumous plants are useful because their root nodules fix atmospheric nitrogen. They may live happily in the fallow bed or anywhere else on your land for that matter.

ALFALFA. Alfalfa, as another popular alternative.

COMFREY is an excellent green manure plant. It is a perennial and will keep going for years if you allow it to. It has a deep tap root system that will bring up nutrients from far beneath the soil surface.

MUSTARD. If you use mustard, a word of warning! It is a member of the Brassica family, so it may spread the disease ‘club root’. So never grow it in the fallow bed! In fact it is probably best avoided altogether unless you intend to confine its use to the brassica bed where it may be sown as soon as your cabbages (or whatever) have been harvested. 

We will be dealing with crop rotation more fully in a future article. The general rule being the green manure plants can be sown as soon as the plot is cleared. This is in addition to the main fallow bed. 

Nature never leaves soil bare and neither should we! It is far better to fill it with a beneficial green manure crop, rather than allow nature to cover it with weeds. 

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