Green manure plants are grown specifically to improve soil structure and fertility. Knowing what soil type you have is key to understanding how to improve it and what plants to grow, or not as the case may be.
In clay soils, green manures can help by breaking up the soil. In silty soils they can be used to protect the soil surface from inclement weather during the cooler seasons and help to improve the structure. On sandy soils where sharp drainage and erosion are a problem, bulky green manures can provide organic matter helping to retain nutrients in the soil.
As I am gardening on clay I have sown Phacelia tanacetifolia in some areas of the garden to help improve structure.
Here are some other benefits of using Green Manures:-
- They can help protect soil life from extremes of temperature and moisture;
- They attract beneficial insects to the garden;
- They take up nutrients that might otherwise be washed away, these nutrients are then returned to the soil when digging in;
- They can act as ground cover and a weed suppressant;
- Some, such as clover, take up Nitrogen from the air and fix it in their roots, in turn adding fertility to the soil, (Nitrogen is an important plant nutrient);
- Others, such as grazing rye, are particularly good at improving the structure of the soil;
- Some can look attractive in the garden in their own right.
There is a green manure to suit most sites, some can be grown very quickly in a matter of weeks whereas others are left for a year or more. Most green manures are actually agricultural crops such as winter field beans, Vicia faba or grazing rye, Secale cereale and as such will compete well with weeds. When using green manures from the legume or brassica families, careful consideration should be given to the crop rotation cycle to avoid encouraging related plant disorders.
Over the coming weeks I will be covering the different plants available as green manures, but if you have any questions in the meantime please don’t hesitate to ask.