Tag Archive: cover crop


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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Phacelia tanacetifolia, a  'green manure' that's good to look at and attractive to beneficial insects.

Phacelia tanacetifolia, a ‘green manure’ that’s good to look at and attractive to beneficial insects.

I’ve just been reading about green manures, from a small prize I won at my induction training as a ‘Master Composter’. The prize is a slim booklet produced by Garden Organic and it focuses on the use of green or ‘living’ manure in the garden. So, what is a green manure?

‘a plant which is grown to benefit the soil, not, as some might suppose, under-ripe animal dung!’

I’ve had a couple of tries with green manure (mainly because I like the flowers of Phacelia), but have not been totally convinced of its value – it’s hard to check what benefits it brings unless you conduct some sort of rigourous trial, of course. Anyway, this booklet is giving me the confidence to do more and so I thought I’d share its contents with you in a short series of ‘bite sized’ articles over the next few weeks.

Apparently green manures have been used by farmers for centuries to improve their land and gardeners have begun to realise their value too. Seed companies have begun to stock green manure seeds in packets sized for the average garden. They are most often used in the vegetable plot, but can also be used in other areas. In later articles I’ll cover where and when to use them; some of the plants and their benefits; how to choose and grow the right plants and what to do when you’re ready to use them. Today I’m focusing on seven reasons why to use green manure.

1.To feed the soil – green manure crops ‘mop up’ and hold onto soil nutrients and some deep-rooted types can actually gather nutrients from depths that other plants cannot access. By absorbing nutrients the roots prevent it being washed down into sub soil. Once green manures are turned into the soil the nutrients are ready to be taken up by the next crop.

2. To protect and improve soil structure – green manures help to protect the soil surface from the effects of heavy rain (mainly soil compaction and surface ‘panning’). This is a benefit for both clay and sand – dominated soils where organic matter reduces compaction in the former and helps water and nutrient retention in the latter.

3. To stimulate soil micro organisms – when dug in green manures feed and stimulate microscopic creatures that in the process of decomposing this organic matter boost soil health, which in turn helps to develop strong plants.

4. To prevent weed invasion – nature abhors a vacuum/ bare soil – as soon as plants are removed new ones will try to move in and these can often be weeds. Green manures tend to germinate quickly so can be a quick way of covering bare soil and smothering young weed seedlings, also eliminating the need for constant hoeing to remove the weeds.

5. To control pests – some beneficial crittters (like frogs and beetles) love the shady, damp ground under a green manure. Some green manures can be planted to distract flying insects away from crops you want to protect; e.g. underplanting Brassicas with Trefoil disguises the outline of the crop and seems to deter cabbage root fly. Likewise a small patch of Phacelia tanacetifolia or Clover, if allowed to flower, will attract insects that prey on many garden pests.

6. To improve the look of the garden – a green manure or ‘cover crop’ will not ony help to prevent weeds but can look attractive of itself. Some also help to fix nitrogen in the soil which will help plant growth.

7. To ‘rest’ your soil – after a period of intensive cultivation, soil can benefit from lying fallow for a season. Most usual in the vegetable garden, it’s a technique that can be useful in the ornamental garden especially where a new border is to be planted up.

Crimson Clover - another green manure that looks good and helps to 'fix' ntrogen in the soil

Crimson Clover – another green manure that looks good and helps to ‘fix’ ntrogen in the soil

So, on paper the case for using green manures is a strong one. My kitchen garden is currently straining under the weight of the many different crops I have growing in every available patch of soil (and some containers too). But in a month or two, once some crops have been harvested, and where I haven’t planned for any new crops, I’m going to put in a green manure. In next week’s article I’ll cover just where and when to use these valuable plants.

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

Old School Gardener

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