Spring: What is it with Green Manure?

Green manures do more than feed the soil and add humus. They act as a vital barrier to what can become fallow ground in winter months and to some extent prevent the need for digging in autumn. At Pig Row we have tried a number of green manures, including rye and phacelia but thanks to a visit to Fir Tree Farm over a year ago we have started to use red clover. We sow this in the first or second week of July between the crops, by the time it has germinated we have taken our harvest and have planted our winter crops. The red clover doesn't compete with the plants but instead benefits many of them as the roots lock in nitrogen from the air. As you can see from the photo below these small plants pack a long root. Over the next fortnight we will cut off the top growth of the red clover with shears or simply by running a lawnmower over the top.

Why we should all use green manures as part of a cycle.


We'll then use a sharp spade (all spades should be sharp but you'd be amazed how many people struggle with blunt tools) to chop into the soil, severing the roots and allowing it to rot down. Two weeks after this we'll hoe the whole area to catch any regrowth. You can immediately plant into the soil if you wish but we always leave two weeks to catch and weed seeds.

Red clover protects the soil over winter

The plus side of such a dense growth on the soil is that it protects the soil from erosion and strangles any weeds, the red clover prevents any minerals, including phosphorous, potassium and nitrogen from being washed away and then provides you with a rich material to add to your soil, improving soil structure. There can be downsides to green manures, some gardeners claim that such foliage gives a perfect home to slugs and snails but we have not found this to be the case. We suspect this is due to the harsh frosts we get on our hillside. There are many green manures on the market, here are just a few that are easy to grow and harvest:

Alsike clover (Trifolium hybridum): a perennial legume. You can dig it in at anytime after two or three months or leave to over winter. You can even dig in after one or two years and it will rot down but remember that all clovers after a long time make a dense mat that requires more work to chop up. This clover is good for wet, acid soils; sow April to August.

Bitter blue lupin (Lupinus angustifolius): a perennial flowering legume good on sandy and acid soils. Dig in after two to three months. We find that ALL lupins are good green manures and we have used vast swathes of them at Pig Row, growing them for two summers and then digging in. Sow March to June.

Red clover (Trifolium pratense): by far our favourite hardy perennial legume. It germinates easily, overwinters spectacularly well and can be left in for as long as you need it to be left in. It's recommended though that you dig it in after two or three months or one or two years. It's good on most soils from acidic to loamy. Sow from March to August. We recommend though that you do it no later then the second week of July.

Grazing rye (Secale cereale): an annual, good for soil structure and can overwinter well. It's good for birds too, as it gives them cover in the garden. Sow August to November and dig in the following March/April.

Mustard (Sinapis alba): we have grown this annual crop with mixed results. As we grow a lot of brassicas we wouldn't recommend it as it can encourage a build up of the disease clubroot. However, if brassicas are not your thing sow from March to September and dig in after two to three months.

Phacelia (Phacelia tanacetifolia): a lovely, bee friendly green manure. Sown from April to August, dig in after three months.

What have we learnt about Green Manures?

  1. Some of them can be sown to protect the soil over winter.
  2. They fix nutrients into the soil.
  3. They protect the soil from erosion.
  4. They are relatively easy to sow and there is a green manure for every soil type. 
  5. Remember green manures are not a miracle solution and you need to include it in a cycle that includes mulching, possible use of animal manure and feeding your soil.

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