In organic gardening green manures are an important way to add nutrients and organic matter to the soil, control weed growth, as well as avoiding disease and pest problems from rotational growing. Every garden bed should have a green manure incorporated (either summer or winter, depending on your crop rotation) at some point in the rotation. It does mean you need more garden area, but very worthwhile to practice. I like to plant a mix of seeds, eg. legumes, cereals and a brassica, believing that diversity is better than a monocrop and it will also confuse potential pests/diseases.
The main aim with green manures is to grow a healthy, leafy, flourishing crop and then dig it back into the soil before it produces – rule of thumb is at 10-15% flowering. Once growth starts to go towards flowering and fruiting, the nutrient value of the crop to the soil diminishes markedly. It can be disheartening to doig a perfectly productive and likely to be high yielding crop back into the soil without harvesting anything, but think how valuable this is for the soil, not to mention the bountiful future crops you will be eating.
Autumn – Sow winter/cool season green manure – usually cereal (wheat, spelt, oats, barley), legume (lentil, pea, broad bean, lupin, annual clover) and mustard (a good disase break) fenugreek, linseed or coriander. Dig in warm season green manure.
Winter – Feed, foliar feed with wormjuice and/or seaweed.
Spring – Dig in winter green manure. Sow summer/warm season green manure – cereal (wheat, spelt, oats, barley), legume (pea, bean, cowpea, mungbean, chickpea, lentil, lucerne), buckwheat or mustard or millet.
Summer – Continue weeding and watering. Mulch
Generally – Pay as much attention to growing a green manure as you would a normal food crop. Allow about 8 weeks for growing and 2-4 for decomposition, before you plant the following crop.
Eating – No, don’t be tempted!