WHAT IS A GREEN MANURE?

What is green manure?

Growing green manures is a technique which has been handed down from traditional agricultural practice. Historically, it can be traced back to the fallow cycle of crop rotation where it was used to allow soils to recover. Nowadays it is a popular organic method of naturally improving nutrient levels and soil structure.

Green manures are used as a type of fast growing ‘cover’ crop primarily grown to add organic matter to the soil. Leaving your land bare of plants can lead to the breakdown of soil particles, leaching of nutrients, and poorer drainage. Green manures will also protect and improve the soil structure – especially important over the winter period – as well as restrict weed growth, and encourage the proliferation of beneficial soil borne organisms. Green manure can also attract native wildlife providing cover and food for predators like frogs, and hoverflies, and - if left to produce flowers - for beneficial insect pollinators.

Typically, a green manure crop is grown for a specific period – usually immediately after one crop finishes but before the next crop is sown - and is then ploughed back into the ground to rot down to release its nutrients. The crop should be cut back before the stems become woody and before flowering to make the most of the available nutrient. At this stage the available nitrogen content is relatively high. Depending on the species of green manure used, you can cut it and just leave it on the soil surface to decompose naturally.

Using plants from the legume family as a green manure will help to accumulate nitrogen from bacteria in their root nodules. They function best in summer, and although field beans and vetches can be sown in autumn for cutting in the spring, summer crops of lupins, clovers and peas will actually add more nitrogen to the soil.

Some nitrogen fixers may be left for more than a year because their root nodules add nitrogen and there’s improvement over time. Of course you would need to rotate green manures as you would any other crop.

Below is a list of popular green manures as well as their planting and harvesting times.

Italian ryegrass - Sow in September - Cut in the spring
Clover - Sow march until August – Cut before flowering
Mustard - Sow from Spring until Autumn between crops – dig in while still young
Grazing rye - sow from August to October - Cut in spring
Winter tares - sow from March to September - Cut in Spring
Winter field beans - sow from September to November - cut in spring at earliest but remain as required.

For related articles click onto the following links:
GREEN MANURES FOR AUTUMN SOWING
HOW CAN YOU IMPROVE CLAY SOILS
HOW TO COMPOST
HOW TO MAKE A LEAF MOULD COMPOST
HOW TO MAKE LIQUID FERTILIZER FROM COMFREY
HOW TO USE BLACK PLASTIC SHEETING FOR WEED CONTROL
RHS: Green Manure
WHAT IS CROP ROTATION?
WHAT IS A DRY MULCH?
WHAT IS JOHN INNES COMPOST?
WHAT IS A LEAF MOULD COMPOST?

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