Mustard produces large volumes of green matter and fibre which can be chopped up and dug in. It is particularly good for soil that lacks organic matter as it helps to improve soil strucure and moisture retention. It is not very hardy but may come through a milder winter, the foliage can be left on the soil surface as a mulch and the remainder can be dug in during early spring.
After 1-2months of growth chop down the plants and dig into the top few inches of your soil. On sandy ground let mustard reach 40cm in height before digging in. This will produce more fibrous plant matter that can help very free draining soils retain more moisture and nutrients.
It is also thought that mustard may reduce the population of wireworms by stimulating the pest to complete their life cycle much quicker, these insects can devastate a crop of potatoes and are useful to use before sowing potatoes.