Green Manuring – Growing and Using Green Manures

Growing and Using Green Manures

green manuring - growing and using green manures This is grow-your-own compost material. A green manure can be any plant grown as temporary groundcover predominantly for improving fertility, either incorporated directly into the soil or composted for use elsewhere. Usually grown on vacant soil over winter, they may also be grown in between crops and incorporated as seedlings. Green manures help prevent soil erosion, the leaching of nutrients and convert otherwise wasted winter sunlight into biomass.

Any plants that grow over winter will do, but those which are easiest to incorporate or which create the most mass are best. Leguminous plants that fix nitrogen from the air are frequently used, as this nutrient is always in short supply.

The manures are usually sown as soon as the ground is bare until the first frosts start. Those surviving the winter are then killed off by impenetrable mulches or digging them in before the crops need the space. Several weeks of breakdown are necessary for some of the more fibrous, such as rye-grass; those that produce succulent growth take far less time. Never let green manures flower and seed or the goodness is lost; it is better to grow two or three short crops of green manure in place of one long one.


Beans and peas

Any variety may be used, but only hardy ones will overwinter. These are pulled up minus their roots before they form pods, thus leaving their nitrogen-rich nodules in the soil. Do not use them in the vegetable plot without considering rotational requirements. ‘Banner’ is a hardy variety of field bean often grown as a green manure.


Lupins

A very useful leguminous green manure, but care is needed as most are poisonous. Lupins improve soil texture, are deep rooting, help improve sour acid land and are generally beneficial — supporting vast populations of aphids and beneficial predators after flowering. Ordinary lupins may be used, but agricultural ones are better and are sown in the spring to incorporate into the soil in the autumn.


Clovers (Trifolium)

Clovers are good for bees if allowed to flower, provide cover to ground-beetles, are hosts to predators of woolly aphids and help deter cabbage rootfly if sown underneath a crop. One of the best short-term leguminous groundcover green manures. However, after a few years land may get clover sick from their own root exudates. Red clover inhibits its own germination when the exudate reaches one hundred parts per million. Before it reaches this level it inhibits vetches, alsike clover and white clover. Clovers in grass sward are helped by cutting the grass higher. Closer cropping encourages first daisies then moss instead. Clovers are poisoned by buttercups, but these can be discouraged by regular liming.

A mixture of red clover and alsike is better than either alone at improving yields of hay. They are rich nitrogen sources, but need a year or two to give full benefit and the clovers are inclined to regrow. Alsike is the best for poor, wet or acid soils; white clover is better on lighter and more limy soils; and Essex red is considered the best for green manuring. Though not as hardy as the others, it does better on loamy soils.


Trefoil

Another legume, similar to clover and related to alfalfa. It prefers a limy soil and is shade-tolerant, so can be used under taller crops. Short lived, it can be sown any time in spring and summer to overwinter.


Winter tares

Vetches are native legumes that will grow in adverse conditions and can be sown from spring till autumn to overwinter. Excellent for producing bulk, fixing nitrogen and suppressing weeds.


Fenugreek

A quick-growing manure that is leguminous and can be sown after early crops, or on vacant land in between other crops. It is unrelated to vegetables, so causes no problem with rotation. It can be sown any time from spring till autumn; then it is killed by the first frosts. It is probably the best green manure for summer use.


Buckwheat (Fagopyrum esculentum)

One of the best hoverfly attractants, this is a calcium accumulator and useful green manure. It has pretty pink flowers and rather straggly growth, but should be grown more often in gardens. It is a quick-growing summer crop that can be left to flower to feed beneficial insects.

Phacelia (P. tanacetifolia) is beloved by bees and hoverflies so should be grown for them anyway. Sow from spring till autumn and it may overwinter. It is easy to remove or incorporate.


Poached egg plant (Limnanthes douglasii)

I find this an excellent green manure as it is hardy over winter, very good at excluding other plants and easy to incorporate afterwards. Some plants left for flower and seed are very beneficial for insects.


Mustard

One of the fastest-growing green manures. If incorporated as seedlings, it can reduce infestations of pests and diseases in the soil, but will not stand hard winters. Grown in between crops or till the first frosts and allowed to incorporate in situ, mustard is very useful. However, being related to brassicas, it must be used with care in rotations and is best grown only to the seedling stage. It can, of course, be grown on for the condiment, but then needs more space per plant.


Lamb’s and miner’s radish (Valerianella & Claytonia/Montia)

Usually grown under cloches for salad leaves, these make effective winter green manures. They’re hardy, unrelated to crops, easily killed and incorporated, self seed fiendishly and are enjoyed by hens.


Hungarian ryegrass

Sown from late summer till mid-autumn it provides quick ground-cover for overwintering and resprouts in the spring. It must be thoroughly incorporated two months or so before the crop to give it time to rot.

04. January 2011 by admin
Categories: Compost and Manures | Tags: , | Comments Off on Green Manuring – Growing and Using Green Manures

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