cover cropMy previous articles on green manure have covered the why, what, where and when –  this final article deals with how to use them to best effect.

Processing your green manure so that the ground can be used again begins around 3 – 4 weeks before you want to make use of the plot for another crop or plant, or alternatively when the green manure approaches maturity – whichever comes first.

There are various ways in which to process the green manure:

  • Dig it in – simply turn the plants back into the soil, using a sharp spade, chopping up clumps as you go. Aim to bury the plants no more than 15cms deep on heavy soils, or 18cms on lighter ground. grazing Rye and perennial green manures can be tough to dig in if they have grown well – to make it easier cut down the foliage first and leave it to wilt and possibly dig the plot twice with a gap of a week or two between each dig.
  • Leave it to the frost – if you sow a frost tender green manure in late summer you can leave this to be killed by the first frost, and the remains can be left on the soil as a cover over winter.
  • Hoeing – annual green manures, like mustard and buckwheat, can be hoed off, leaving the top growth in place or added to a compost heap. You can plant through the green mature foliage or cultivate it further to create a seed bed.
  • Mulching – a light excluding mulch can be used to kill off the green manure – black plastic or large sheets of cardboard held down by straw or bricks etc. Annual green manures will die off in a few weeks whilst perennials and grazing rye will take a bit longer – but you can always plant through the mulch.

No Dig = no green manure?

You may garden using the ‘no dig’ method. If so, you migth feel that grazing rye, even though it is an excellent soil improver, should be avoided. However, you can cut down the rye, spread it with well-rotted manure if required and then plant a crop of ‘no dig’ potatoes on the surface. these can then be covered with a mulch of hay or straw (around 10cm deep) adding more of this as they grow, and topping off with layer of grass mowings before the potato foliage meets across the rows.

Too tough to dig in?

If you forget to deal with your green manure in time and it becomes tough and woody, don’t worry. Just cut off the tops and put them on the compost heap, then dig in the roots or cover with a thick mulch.

Timing is everything…

If you dig in young annual green manures during the summer they will decompose rapidly, leaving you able to plant up the area within a few days of digging in. Tougher plants, like grazing rye, need to be dug in a few weeks in advance of when you need the ground again, especially in spring when decomposition is slower. If you’re aiming to create a fine seed bed after your green manure remember to leave the ground for a longer period than if you are simply planting into the ground. And avoid using green manures where you plan to sow small seeds such as carrots, parsnips and spinach as some green manures have a chemical which inhibits germination.

I hope that these articles on ‘Green Gold’ have been useful, and that you’ll be using green manures in your garden. I’m certainly planning to build on my early experiences last year with sowing more green manures over the coming winter.

Phacelia in flower

Phacelia in flower

Source: ‘Green Manures’- Garden Organic Guide. September 2010

Other articles in this series:

Green Gold: 12 plants for soil improvement

Green Gold- 7 reasons to use green manures

Green Gold: Where and when to use Green Manures

Old School Gardener

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