Conventional green manure includes species and varieties not grown for
organic nematode control. The most important species are mustard and radish, as
well as all species grown for feed as well as to provide green manure.
The crops, such as buckwheat, are very fast-growing and make an important contribution to the farm's humus balance.
White mustard is a cruciferous plant, and is divided into nematode-resistant and conventional types. All white mustard varieties are suitable for mulch sowing, as they generally die back in winter. This property means that mulch sowing is becoming more popular. There is a considerable difference among white mustard varieties when it comes to flowering times. The range extends from 15 September to 27 October, starting in mid-August. As a green manure plant, white mustard also removes large quantities of nitrogen from the soil. It does not tolerate frost and so is certain to die back during winter. The plant is sometimes known as yellow mustard because of its bright yellow flowers, but is more usually called white mustard because of its white seeds.