When vetch is grown as a winter green manure it is common practice to break the crop down and mix it into the topsoil. As it decomposes vetch releases toxic compounds that will inhibit the germination of seeds so the sowing of a drilled crop should be avoided for at the very least two weeks and preferably up to 4. It is possible to establish a transplanted crop in a much shorter time although some transplanted crops could be at risk if only a day or two has gone by. Sweetcorn and dwarf French beans can be particularly susceptible while leeks were unaffected. The effects in both cases will be influenced by the lushness of the foliage at the time of incorporation. If a vigorously growing crop of vetch is worked straight into the soil the effect will be greater. Cutting and wilting the foliage should reduce it. Leave a week after incorporation before planting to be on the safe side. The dilemma is that as the unpleasant compounds are released so is the first flush of nitrogen. Vetch is probably the worst common green manure in this respect.
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