A selection of green manure crops
The crops most commonly used for green manuring include annual lupins, buckwheat, Hungarian grazing rye,, rape, winter and winter tares, or vetch.
Mustard, which has the advantage of being quick-growing, is a good choice for light sandy or gravelly soils, as are lupins and rye. On medium loams, a number of crops should give good results, including rape, rye, lupins and winter tares. For heavy clay soils, winter tares are most suitable. In each case, a mixture of the appropriate crops will also give excellent results.
The annual lupin that is used for green manuring is Lupimis angustifolius. Sow the seeds between mid-spring and midsummer, 15 cm (6”) apart, in rows similarly spaced and at a depth of 7.5 cm (3”): 120 g (4 oz) of seed is sufficient to sow ten 10 m (30’) rows, or an area of about 15 sq ft (165 sq ft). Allow the plants to grow until the first buds appear, then tread them down and dig them in before they flower. In goodthey may reach 1.0-1.2 m (3-4’) in height, when they can be dealt with most easily by running a roller over them. They are legumes and fix nitrogen in their roots, so there is no need to dress the soil with a nitrogenous fertilizer.
A few plants may be allowed to flower and go to seed, for later use. By this time, their stalks are too tough for use as, but they can be put into the heap.
Buckwheat fagopyrum esculenturn) is a quick-growing crop which is grown to make flour and animal feed in North America and parts of Europe. It also makes an excellent green manure crop and is especially useful for improving the water-holding capacity of a light sandy soil. Sow the seed 7.5 cm (3”) apart, in rows about 25 cm (10”) apart: 30 g (1 oz) should be sufficient to sow three 10 m (30’) rows, or an area of 9 sq m (100 sq ft). Be careful not to sow too thickly, or the plants will be overcrowded and the resulting crop poor.
You can sow the seed at any time between mid-spring and mid-summer.
When the plants are about 60 cm (2’) high, and the leaves are still green, flatten the buckwheat with a roller or tread it down, spray it with water and sprinkle it with sulphate of ammonia at the rate of 60 g per sq m (2 oz per sq yd) before digging it in.
Digging in should usually be done in late summer. The leaves, however, should not be allowed to start yellowing, because this indicates that the stalks are getting tough and will not break down easily in the soil.
Some gardeners sow annual lupins and buckwheat in alternate rows, so that when they are dug in together, no additional source of nitrogen need be provided.
Hungarian grazing rye
In small, intensively cropped gardens it is usually only during the winter that there is any uncropped soil available for green manuring. A good crop for such situations is Hungarian grazing rye, which is particularly tolerant of a fairly cold climate, having been bred for winter grazing. The variety that is normally grown is Lovazpatoni.
It should be sown at any time from the end of late summer to the end of mid-autumn. Sow the seed broadcast at the rate of 30 g per sq m (1 oz per sq yd) in soil that has been raked level (after having been dug and hoed), as is done when making a lawn. Scatter the seed as thinly and evenly as you can.
Alternatively, you may find it easier to sow the seeds, which are quite large, 5 cm (2”) apart in drills 10 cm (4”) apart. This method will be found to be more economical of seed.
The rye will be ready to dig in by mid-spring when it should be between 30 cm (12”) and 45 cm (18”) tall. You should then tread it down, moisten it with water from a watering can or hose, dress it with a nitrogenous fertilizer at the rate of 60 g per sq m (2 oz per sq yd) and finally dig it in. Rye is particularly effective as a green manure on light sandy soils. If space allows, it is worth growing an extra row to provide seed for your green manure crops for the next season.
This is probably the most popular green manure crop for vegetable gardens. It is quick-growing and can thus be dug in after a very short period, typically no more than 4-1/2 weeks. This makes it particularly useful for growing as a catch-crop and also during the very short periods when a plot may be vacant during spring and early summer. If a more prolonged period is available, the manuring can be intensified by growing and digging in successive crops of mustard.
Mustard should be broadcast-sown thinly at the rate of 3.5 g per sq m (1/8 oz per sq yd) between mid-spring and mid-summer, or even as late as the end of late summer, if any space is vacant. As soon as it is about 30 cm (1’) high, and before any flowers have appeared, it should be trodden down, moistened, sprinkled with a nitrogenous fertilizer at the rate of 60 g per sq m (2 oz per sq yd) and dug into the soil.
Mustard has the advantage of being cheap and available from most garden shops or nurseries. However, because it is a member of the brassica family, it has the disadvantage that there is a risk of introducting clubroot disease, which is a most serious fungus disease affecting cabbages,, Brussels sprouts and other brassicas. Mustard should not therefore be grown in gardens where clubroot is known to occur, or it may pass the disease from one brassicas crop to the next.
This is another member of the brassica family and might therefore encourage clubroot. However it has the advantage of being as fast growing as mustard and should be grown and treated in much the same way, except that the sowing rate is only 2.5 gper sqm (1/12 ozper sqyd). It can be sown up to the beginning of mid-summer.
Winter spinach is another crop for green manuring during the winter. Again, it has the advantage that the seed is easily obtainable from garden shops or seed-men. If the space is available, sowing can start in late summer and early autumn.
Sow the prickly seeds 7.5 cm (3”) apart in drills 2.5 cm (1”) deep and about 30 cm (1’) apart. 30 g (1 oz) of seed is enough to sow twelve 3 m (10’) rows. When the crop has reached about 25 cm (10”) tall it should be trodden down, moistened, sprinkled with sulphate of ammonia at the rate of 60 g per sq m (2 oz per sq yd) and dug in.
This form of vetch, which will survive the winter, is possibly the best green manure crop of the pea family. One of its advantages is that it can also be sown in the spring on vacant sites in the kitchen garden which are awaiting later crops.
For winter green manuring, sow it at any time between late summer and mid-autumn for turning under in early spring and mid-spring the following year. You can also sow it between early spring and late spring for digging in during mid-summer, when the flowers are just in bud but showing no colour.
Sow the seed 7.5 cm (3”) apart in rows 15 cm (6”) apart. You will find that 30 g (1 oz) of seed is sufficient for eight 3 m (10’) rows, or an area of about 4.2 sq m (45 sq ft). Alternatively, you can broadcast the seed at the rate of 3.5 g per sq m. Some plants can be allowed to go to seed to provide for future use.
Being legumes, winter tares fix nitrogen, so there is no need to dress them with a nitrogenous fertilizer when digging them in.