What is green manure?

Perth sandy soil is lacking in a lot!  One key thing we don’t have much of is organic matter.  Green Manures are crops grown specifically for turning back into the soil to increase its organic matter content (provide humus).They also help to control weeds in otherwise ’empty’ garden beds, preventing soil erosion and helping to prevent nutrients leaching.  Living plants in a garden bed help preserve moisture in the soil by keeping it active – soil microbes need plants to survive.  Empty beds can become devoid of life – although nature tries to take care of this by providing weeds to fill the gaps!!

Many plant species are suitable for using as green manure; usually things that provide lots of fast growing leafy material, and plants that are nitrogen fixing are highly beneficial.

Green manure can help with root knot nematode by increasing organic matter in the soil generally.  If you have heavy infestations – grow a crop from the brassica family (mustard is ideal as it is fast growing), thickly planted & slashed back into the soil. As it decomposes, compounds released from the plants act as a bio-fumigant, suppressing root knot nematodes.

A green manure crop is grown for as long as you want to leave it there – usually until they begin to flower (you don’t want to create weeds by letting seeds mature) and slashed.  They are allowed to rot down and feed the soil before planting a ‘real’ crop.  Of course, you can use green manure crops & dig them in when they’re much smaller; obviously smaller plants mean less organic matter – but it may be a question of timing if you need to utilise the garden bed.

Ingredients of the packs will differ depending on the time of year to make sure there are suitable varieties of seed for Autumn & Winter, and Spring & Summer.  But we try to ensure a wide range of variety so that several species will thrive.

Variety is the key – legumes, grasses, brassicas etc. all provide benefit – some varieties in the mix will always do better than others (depending on conditions).  Plant green manure thickly at a ratio of approximately ½ kg per 10m2.

Allow to grow for approximately 8-10 weeks then slash before flowering (and setting seed) and allow to break down in the garden bed before planting your vegetable crop.

For an ‘express’ green manure, allow to grow for only 4-6 weeks, then slash.  Throw on a few handfuls of blood & bone to aid breakdown, water, then cover with black plastic for two weeks.  After this, the crop should be broken down enough to be turned into the soil.

Benefits:

• Ideal soil improver
• Natural soil fumigant
• Creates organic bulk and humus
• Soil microbe enhancement
• Insect and disease inhibitor
• Easy to handle and establish
• Reduce water evaporation & drainage