Green Manuring for Soil Fertility

Green Manuring for Fertility

While green manuring is most often thought of as a method of increasing soil fertility on smallholdings and larger acreages, it can also be done very successfully in the ordinary garden. Perhaps the most difficult problem is to be able to buy fairly small quantities of seeds, although they can now be secured more readily than was once the case. I have used green crops for improving soil fertility conditions in gardens and allotments in various parts of the country, and they have never failed to improve the ground and to make it possible for good results to be secured. There have been heavier crops of good flavoured vegetables and flowering plants, free from diseases and disorders, with blooms of good colour and texture.

thick growth of green manure crops

Green manure plants are among the best natural soil conditioners. They improve soil tilth, chiefly by aeration and make it easier for other feeding agents in the soil to become readily available to plants. Green manure can be said to grow humus which prevents plant foods from being washed out and in the case of legumes, they increase soil nitrogen without causing soft leafy growth, or encouraging edible crops to run to seed prematurely.

If in naturally clay soil, the green manure crop is well worked in, it will break down quite fast and render the soil easier to work. Especially where there is not enough compost available for the whole garden area, a good biological fertility action can be built up with resistance to disease or pests by green manuring.

While it is possible to use certain annual weeds as a green manure crop and many of them are really fast growing succulent plants, some are liable to seed when quite small and a continual crop of self sown weeds can become a nuisance.

Green manuring is nature’s method of gaining or increasing fertility and has many advantages. Whenever a piece of ground can be allowed to lie fallow for a period of six weeks or more of growing weather, the site can be dug or hoed deeply, and quick growing seeds to grow plants that make ample foliage can be used. These include, peas, beans, lupins, tares, all of which will add nitrogen to the soil. In addition, any flower and vegetable seed you have surplus to your needs will also help to make first class green manure if they are dug in when they are in leafy growth.

Mustard is often used and it is one of the best plants to grow when, for instance, one is using fresh land which has been stripped of top soil by nearby building operations, and one is left with an exposed lifeless subsoil. One should beware of using mustard where club root has been prevalent in a recently harvested crop. Since it belongs to the order cruciferae, it is liable to be attacked by club root fungus.

If dried sludge is dug in before mustard seed is sown, growth will be succulent and free. Although the humus that mustard supplies is not lasting, it is of special value when one is taking over a new or neglected site where the soil is dry and more or less lifeless. Since it is a quick growing crop, where the garden is not being used for some months, it will be possible to make two, perhaps more, sowings in the year.

Sunflower seed too can be highly recommended if the land is not being used for several months in early summer. This crop must be dug in before the stems become too tough, otherwise and they will take a long time to decay.

Lupinus augustifolia The blue field lupin, Lupinus augustifolia, has often been used as a green manure crop. The white flowering form is equally good. They are quick growing and ideal for sowing in spring or summer. Dig them in as soon as the {lower spikes can be seen and while the stems are still fairly soft. It is helpful to first knock down the growths before chopping them up and putting them in the trench as digging proceeds. Any plants not dug in can be placed on the compost heap. The seed should be sown in the spring, spacing the rows 90 cm apart, and finally thinning the plants so they stand about 75 cm apart, in the rows. It is advisable to take out the growing points to encourage bushy plants to develop. The stems sometimes become very hard and when this is so, they should be broken down and the toughest pieces placed on the compost heap, rather than digging them in.

Winter Tares are often sown in late summer, but they are equally suitable for sowing in spring when they can be dug in during the summer.

Buckwheat, Fagopyrum esculentum is another useful green manure crop. Since it is not a legume it is not attacked by club root disease. The seeds are large and are best sown in rows a foot apart. One ounce of seed will sow a row 30 metres long. Sown in spring, growth becomes very leafy, so much so that all except the coarser, more persistent weeds, such as ground elder, are smothered.

Crimson Clover - Trifolium incarnatum Crimson Clover, Trifolium incarnatum, is usually of annual duration and not to be confused with the clovers most of us like to keep from our grass lawns. If left it will grow 20 to 24 inches (50 to 60 cm) high and as a bonus it will, if allowed to flower, be of use to bees which never fail to find and regularly attend the plants. For this reason, crimson clover is often grown near beehives. Sow the seed in April making sure the site is not lacking in lime.

The rate of sowing varies, but as a guide, mustard and vetches can be used at the rate of 1/16 oz lupins 1/8 oz, peas and other coarse seeds 1 oz all to the square metre.

Growth is usually quick and the normal practice once the flowers begin to pass over is to break down the stems and dig in the plants. If you can afford the space and the soil fertility is in really poor condition, the site can be re-sown with the same crop again, which however, will mean that it will not be possible to use the land for an edible or ornamental crop until the following spring. Another way of using crimson clover is to sow it in August or early September after a crop such as potatoes has been lifted.

Whatever green manuring crop you decide upon, every endeavour should be made to take out deep rooted persistent weeds such as couch grass, ground elder, convolvulus, thistles, and docks before turning in the sown crop.


22. August 2010 by Dave Pinkney
Categories: Garden Management, Manures and Fertilisers, Neglected Gardens, Soil Cultivation | Tags: , | Comments Off on Green Manuring for Soil Fertility

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