Green Manure - Natures Own Compost

Mustard (Sinapis alba)

Mustard is great if you want a quick-growing green manure, and can be sown from March right through until about September time (depending how far north you are). When grown late the bees seem very thankful for flowers during the dying months of the year. It grows very quickly (in about 1-2 months) and is particularly good for soils that lack organic matter due to its fibrous content, which helps give structure to fine soils when dug in. What's more, as mustard leaves are edible they can be used as crop too.

I tend to follow a potato crop with mustard seed as it can help rid the area of wireworm. Grow until the first flowers appear then dig in. Sow thinly in 15cm rows, 3-5g per sq metre.

Winter Tares (Vicia sativa)

Sow in the spring, late summer or early autumn and it will be ready to dig in after 2-3 months. It won't give much ground cover if sown in the autumn as it grows slowly so don't expect it to keep the weeds down for you. Winter tares is not a big fan of acid or overly dry soils but will tolerate most others, and will fix nitrogen in the soil. It should be sown, not broadcast, at a rate of 20g per sq metre.

Alfalfa (Medicago sativa)

Alfalfa is in the pea family and might already be known by many as one of the seeds in sprouting mix. Sow between late spring and the middle of summer - it will take about a year or more to grow. Indeed given the optimum conditions it can live for up to 12 years!

This makes alfalfa an ideal crop to sow on a patch of earth that may not be cultivated for some time. Many allotment societies will have a rule concerning how much of a plot must be used to be deemed to be under cultivation, and, as alfalfa can be sown and left, it will be considered by most as using a plot, thus keeping the officials off your back! However, it should be cut back two or three times over a year to encourage new, fresh growth. Broadcast at 2-3g per sq metre.

Phacelia (Phacelia tanacetifolia)

Phacelia is a beautiful plant with vivid blue flowers and can also be grown on a wildlife-friendly plot in order to attract bees and hoverflies. When used as a green manure it should be cut down before it flowers. It can be sown in early spring and then dug in after about two months or planted in late autumn to be dug in during spring.

Phacelia will thrive in most soils and as it is a bushy plant it should also act as a weed retardant. It is not frost hardy and many of my plants have died off during this cold winter (2009-2010), however it has kept the weeds down and the dead plants have now been dug in. I will allow one or two of the surviving plants to mature before cutting back in order to obtain seed for the next season. Broadcast sow at a rate of 2g per sq metre.

Hungarian Grazing Rye (Secale cereale)

I have sown this in October before, but only because I live in the south of England. Further North it will be safer to sow by September. Hungarian grazing rye is left over winter and its dense, grass-like foliage is enough to frighten off most weeds. Sow thinly in rows 20cm apart - or broadcast the seed at a rate of 16g per sq metre.

Trefoil (Medicago lupulina)

Sow in spring to late summer and Trefoil will make a good ground cover for the winter months. It will take around 3 months to grow and will withstand most light and dry soils. Trefoil will not tolerate acid soil. It is a low-growing plant and can be intercropped with taller crops such as maize.