Green manuring is a great way to fertilise and increase the organic matter in your soil. Green manuring is an organic soil improvement method using a crop of mixed legumes and grains. The whole plants are harvested by ploughing the young plants into the soil just before they flower, investing the soil with nitrogen, organic matter and new life force.
Legumes are plants in the bean family which have a unique association of bacteria which can extract nitrogen from the atmosphere. Grains, which are types of grasses, are also used because they produce a lot of green matter quickly which on breaking down becomes soil carbon, or humus. So what we are doing here is a method of composting in-situ which can easily be done over large areas as well as backyard garden beds.
Green manure can be sown almost anytime of year but the plants used will depend on the season and your climatic zone. For seeds and information on warm and cool season green manure planting, have a look at Greenharvest (Australia) or TurtleTree Seed in North America or go to a stockfeed supplier if there is one in your area.
As a Winter garden is usually smaller in terms of productive plants, Autumn is a good time to sow on unused or exhausted soil to prepare it for your next Spring planting.
The time for breakdown varies with temperature and soil moisture, but it is usually around six weeks. Check there are no lumps of rotting vegetation before planting again.
An alternative no-dig method is a green manure mulch. Simply mow or slash the green manure and use as mulch.
More info: http://backyardbiodynamics.com/?p=586