Download a copy of the Green Manure factsheet here.
Green manures are sown into ground between crops by gardeners and fresh-market producers, usually during autumn and early winter, although they have application for spring and summer in some situations. Green manures are most often used for vegetable cropping rotations but may also be used for preparing ground for ornamental gardens, or more broadly to improve ground for following crops in agriculture generally. There is also wide-spread adoption in vineyard and other perennial horticultural enterprises.
Nutrient sink – captures nutrients that may otherwise leach away below the cropping zone
Less reliance on artificial fertilisers
Often less irrigation needed on subsequent crops
Soil stabilisation – helps avoid erosion where soils may be bare or fallowed
Increased fertility – adds significant amounts of soil organic matter
Nitrogen Fixation – Lupins, peas, vetch, clovers and tic beans obtain nitrogen from the air and it becomes available to subsequent crops
Planting: late summer to early spring
Analysis by weight
Faba Beans 30%
Field Peas 20%
Add 5% by weight of phacelia, mustard, rape or tillage radish if these additional species are desired.
Suggested sowing rates
2–3 good handfuls per square metre = about 30–50 g/m2
e.g. garden bed 5m wide x 10m long
= 50 m2, 50 x 50g = 2.5kg required
Broader scale applications
200–300 kg per hectare
= about 75–125 kg per acre
Management and use patterns
Whilst many annual plants including weeds may offer some benefits as green manure, species should be selected that will establish vigorously for the time of year planted and be readily incorporated into the soil. The Green Manure Blend is suitable for crops grown in cooler times of the year, and sub-tropical species will only suit early summer planting. Whilst one of the main roles of a green manure is to capture nutrients to make them available for subsequent cropping, there will in many cases be sound cause and justification to apply some form of fertiliser where elements may be lacking and thus impact growth potential. A soil test and reflection on recent cropping history will offer guidance.
Generating biomass quickly is a key for success. Crops should be sown at seeding rates that assist with developing a quick ground cover, bearing in mind that we are not seeking to grow the crop to full maturity. Best results are achieved if the crop is relatively young, lush, and vegetative when it is time to finish it up. Typically allow for around 8–10 weeks growth before slashing, mulching, or digging in. The crops should be leafy and tender at around 40–60 cm high with full groundcover at time of incorporation. Allowing crops to get taller may increase their fibrous nature: the crop may be more difficult to manage, and there may be unsatisfactory amounts of stem and other residue remaining.