Green Manure Crops

Green Manure crops are crops which are sown and grown on land which is laying fallow with the express purpose of digging them in so that they will improve your soil. There are two very different types of green manure – those which fix nitrogen inthe the soil and those which do not do so. The one you choose will depend mainly on the nature of your soil and the length of time you are going to leave it to grow.

Green manure plants that act as nitrogen fixers include: Alfalfa (Lucerne); Broad or fava beans; Red clover; Lupin and winter tare. Green Manures which do not fix nitrogen include: Buckwheat; Rye; Phacelia; Mustard and Italian Ryegrass.

Italian Ryegrass is a particularly useful plamt as you can sow it early in the spring and it will quickly germinate even in cold soil. It is fast-growing and bulky. So you can sow it very early and dig it in before the ground has warmed up sufficiently to plant out tender vegetables. Be careful though, you must ensure you use the annual strain called “Westerwolds” and not the biennial or perennial ryegrass. You must also be sure to dig it in before it produces seed.If you sow the wrong type of rye grass, you will never get rid of it.It will keep regrowing no matter how many times you dig it out. The latin name for Italian ryegrass is Lolium multiflorum.

Phacelia (Latins name:Phacelia tanacetifolia) is one of the best green manure crops in spite of the fact that it does not fix nitrogen. It does not rob the soil of nutrogen either. It does not withstand cold, so sow it after the threat of frost has passed and dig in after about eight weeks.

Buckwheat¬† is useful only where you have space available for the whole of the summer (most of us haven’t) Sow when it is warm in the spring or early summer and dig it in in autumn. Buckwheat is tall and has a very extensive rot system. It makes loads of organic matter but does not fix nitrogen. To add to its advantage: it attracts hoverflies which eat greenfly by the thousand.

Mustard is very useful since it is very quick growing and is a good weed supressor. It is shallow roted so is easy to dig in. Sow in spring or summer and dig in autumn before it flowers. The snag with mustard is that it is a member of the cabbage family so it could harbour club root.

Broad or fava beans is a really super green manure crop. It will stand the winter weather almost everywhere. It produces loads of organic matter and fixes nitrogen. Sow in autumn or early summer, harvest the beans then dig the rest of the plant in.

Lupin is a deep rooted legume which adds nitrogen and large amounts of phospherous to the soil. Sow in spring and cut down and dig in in summer.

Red clover has an extensive rot system that will supply plenty of organic matter. It is low growing and a good nitrogen fixer, It is best to sow it in spring or early summer but always before autumn. Dig in when the land is needed.


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