About green manures
The soil is at the root of nearly all gardening problems. Gardeners who neglect what happens beneath the surface of the soil are invariably disappointed with the development of foliage, the formation of fruit and the eventual harvest.
It is the soil that holds the nutrient, water and air that plants need to thrive. Growing a green manure crop is an easy, inexpensive and low maintenance way of improving the health of the soil. These crops have many benefits.
Green manures not only increase the organic content of the soil, but also add valuable nutrients such as nitrogen and phosphorus. They can also provide an organic mulch that suppresses weeds and improves the soil’s ability to hold water.
Avoid leaving your garden beds bare this winter, sow a green manure crop to prepare your soil for the spring rush.
Benefits of green manures
- Adds organic matter to the soil, which supports microorganisms and worm activity as well as improving water holding capacity.
- Adds additional nutrients such as nitrogen, phosphorous and carbon.
- Helps to stabilise the soil and prevent leaching of existing nutrients during heavy rains.
- Protects the soil from harsh baking sun that could otherwise kill off existing soil micro-organisms.
- Improves soil structure through root penetration which also increases available oxygen.
- Smothers weeds and provides competition against opportunistic weed growth.
The science
- Plants absorb carbon from the air during growth and use it to build their roots, stems and leaves.
- Deep rooted plants also take up nutrients from deep in the soil profile, making them available to shallow rooted plants.
- Bio Mustard is a mixture of mustards with high isothiocyanates, a suppressor of fungal growth and destructive nematodes once dug in.
- Legumes work with bacteria to convert nitrogen from the air and store it in the soil.
How to grow and use green manures
Select a bed or range of gardens beds which you would like to prepare for sowing or growing in several months time. It could be a new garden bed, or part of your crop rotation.
1. Sow and grow
- Prepare a weed-free bed.
- If your green manure mix comes with inoculant, you can either lightly dampen the seeds before sprinkling with inoculant and make sure the seed is thoroughly coated and sown within 24 hours, or, the inoculant can be applied after sowing by diluting in water at the prescribed rate and watered in using a watering can.
- Sow the seeds just under the soil surface, lightly raking soil back over the seeds, and water in well.
- Water regularly once germination starts, as you would any other crop. Most green manure mixes include a range of fast-germinating seeds to out compete weeds during establishment.
2. Cut back
- Cut green manure back before flowering. This is usually done at 8-10 weeks, although it can occur at any stage.
- The top growth can be used as mulch, added to your compost or incorporated into the soil.
- Green manures are typically dug into the soil in order to sequester the stored nutrients.
3. Dig in
- Dig into the soil and leave at least 4-6 weeks prior to planting to allow the green manure to decompose prior to planting.
- Green manures can be dug in at any stage of growth up to the flowering stage (avoid allowing plants to set seed).
- Your soil is now enriched, invigorated and ready to plant.
