Caliente mustards have been developed as green manures with biofumigant properties. Biofumigation refers to the suppression of various soil borne pests and diseases by naturally occurring compounds. These are produced when the crop is chopped and incorporated into the soil. The effects include improved soil structure and fertility, suppression of various soil-borne pests and diseases and increased soil microbial activity. A wide range of brassicas and Eruca (rocket) species have this effect. Ordinary mustard sold as a green manure or from oil seed rape seed sold in pet food stores is reported to be much less effective.
Cultivation
Sow spring to late summer for a quick crop (roughly 60 to 90 days from sowing) To cover areas of bare soil over winter sow early to mid October in areas of moderate climate, the crop will be ready for incorporation in early to mid spring. In areas of prolonged hard frost there may be some plant death and covering with fleece in these areas may be beneficial.
The effectiveness of this mustard is dependant on the soil being warm. A soil temperature between 10-15°C (50 - 59°F) is ideal, and autumn or late spring incorporations are the most effective. Incorporate the crop into the soil ideally when all vertical growth has stopped, if the crop is allowed to flower, allow up to two weeks after first bloom for maximum biofumigation effect. Ensure that the crop is incorporated before seed pods turn brown. Leave for 14 days but then replant as soon as possible after this to gain the greatest benefit.
To be most effective the mustard needs to be chopped and incorporated into the soil and the area covered with clear polythene. The chopping of the plant material produces a biofumigant called isothiocyanate (ITC) which has an effect in reducing and suppressing a range of nematodes and soil borne diseases. Two compounds (glucosinolates and an enzyme) combine to produce the ITC gas. The release of isothiocyanate is dependant on chopping up the mustard – the finer the chop the greater the effect. In a garden situation this could be achieved with a rotary mower followed by rotovating to incorporate the vegetation into the top 15cm (6in) of the soil. Good results are reported using a strimmer or garden shredder followed by digging. The surface of the soil must then be immediately sealed to retain gaseous products using polythene.
Caliente mustard is available in RHS plant centres from mid-February and online from Tozer Seeds
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