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What are Green Manures?

Green manure, love your soil, what are green manures

Green Manures, also referred to as fertility building crops, may be broadly defined as crops grown for the benefit of the soil. A wide range of plant species can be used as green manures. Different ones bring different benefits. If the most is to be made from green manure crops it is important that they are carefully integrated into the crop rotation and proper attention paid to their cultivation.

Advantages -

  •  Increased biological activity
  •  Improved soil structure and drainage
  •  Reduced erosion and leaching
  •  Increased supply of nutrients available to plants (particularly by adding nitrogen)
  •  Weed suppression
  •  Reduced pest and disease problems
  •  Can provide food and shelter for insects
  •  Can provide supplementary animal forage

Summer green manures -

These can be legumes (for a quick boost of nitrogen in mid rotation) or fibrous (buckwheat or green-manures-as-a-way-of-managing-weedsphacelia). They may be grown for a whole season (say April to September) or for a shorter period between two crops, or between widely spaced plants.

Winter green manures -

These are sown in the autumn and incorporated in the following spring. They can be a good way of fitting a fertility building crop into a rotation if they can utilise land that would otherwise be bare. Must be sown before the end of September.  For more information on Winter Green Manures , please click here.
What is essential is rapid early growth and the development of an effective root system. Large quantities of nitrate can be lost from soil which is left bare overwinter. This is because, unlike other nutrient ions, nitrate is not strongly attracted to soil particles. Any that is in solution in the autumn will be washed away as water moves down through the soil with the onset of heavy winter rains. One of the best ways of preventing nitrate leaching is to sow and maintain a vigorously growing crop over the winter.

Where to use green manures

  • On empty beds, whatever the time of year. Good when potatoes or onions come out as the soil is already prepared.
  • On areas of low fertility.
  • On areas of poor soil structure.
  • Between widely spaced plants – eg winter brassicas/sweet corn.
  • On fallow areas not at present in cultivation.
  • Never leave soil uncovered - aim to have 100% groundcover, 100% of the time.

How to sow

  • Prepare a level seed bed, reasonably weed free for best results.
  • Scatter seeds on top and lightly rake in.
  • Water if weather is dry.

Incorporation into the soil 

This should be done four weeks before you need the soil or before the Green Manure plants becomes woody, whichever comes sooner. You can -

  • Cut down with strimmer or scythe and leave soften on the ground.
  • Dig the plants back in using a sharp spade. Aim to bury them between 15/18 cms deep.
  • If a frost tender manure is used in late summer you can let the cold weather kill it off. Leave on the soil, no need to dig in.
  • Annual green manures such as mustard or buckwheat can be hoed in. Excess foliage can be composted.
  • Mulching works well  - annuals will take a few weeks to break down while perennials and rye will take a bit longer.
SEED   CHARACTERISTICS  COVERAGE
Summer
Red clover High yield, n fixer, deep rooting, improves soil structure 400m2
Alsike clover   quick growing, n fixer, suitable for wet conditions & low ph 800m2
White clover N fixer, suitable for under sowing 800m2
Crimson clover Quick growing annual, n fixer, attracts bees.  Beautiful flowers 300m2
Lupin Quick growing organic matter 60m2
Summer vetch N fixer, organic matter 100m2
Buckwheat Catch crop, attracts bees, weed suppresor 140m2
Mustard Catch crop, fast growing 400m2
Sunflower Catch crop, attracts bees & birds 300m2
Phacelia Organic matter, attracts bees, lovely flowers 600m2
Fodder radish Deep roots, improves soil structure.  Weed suppressor 400m2
Winter
Rye Deep rooting, hardy - sow until november 50m2
Rye/winter vetch For late sowing, n fixer 60m2
Phacelia/w vetch Quick weed suppressor, n fixer 225m2
Rye/phacelia For later sowing 70m2
Landsberger mix wInter vetch, crimson clover, westerwolde/italian rye grass Deep rooting, good cover, n fixer, can be used for fodder.  Prolific Growth 160m2

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