Growing green manures

Green manures are an easy, cheap way to produce organic matter for soil by growing grains until they are knee high, or inoculated legumes* until they start to flower, then slashing them, and leaving them, as organic mulch, on the soil surface to break down, or slashing them into smaller pieces and digging them into the top 10 cm of soil. Suitable green manure crops for each season and climate zone are included in ‘What to grow’ that is posted on this blog each month.
For those unfamiliar with growing green manures, step-by-step guides can be found in my book, Easy Organic Gardening and Moon Planting, or in the March/April 2008 issue of Warm Earth magazine.
If planning to use the bed immediately after slashing the green manure, digging fresh, organic matter into topsoil can cause a temporary nitrogen deficiency, as soil bacteria require nitrogen to break down the materials, then nitrogen then becomes available for your crops. Apply some complete organic fertiliser to the bed so that nutrients are immediately available to your plants.
* Inoculating legume seed enables the legume to fix nitrogen efficiently by introducing the nitrogen-fixing bacteria to soil. Uninoculated legumes can be still be grown as green manures to supply organic matter. (See post on Fixing nitrogen.)

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