Seeds of Black mustard, rai (Rhamphospermum nigrum)
Black mustard from seed
Rai is the small dark mustard seed you hear crackling in the pan at the start of a South Indian dal or sambar. It comes from a tall, branching annual with bright yellow four-petalled flowers and slender pods. Its current botanical name is Rhamphospermum nigrum, though most books still list it as Brassica nigra.
Height
60-120 cm, spread 30-60 cm
Seed
dark brown to black, about 1 mm
Germination test
alternating 25/15 °C (USDA genebank)
Hardiness
Annual; autumn sowing possible where winters are mild
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How to sow
- Scatter the seed thinly and rake it in lightly; any moist bed with free drainage and sun or part shade will do.
- It germinates readily in mild conditions, around 15-25 °C.
- Thin to give each plant room, as it can reach 120 cm and spread to 60 cm.
- Where winters are gentle it can also be sown in autumn.
Growing in Europe
Black mustard grows easily across Europe as a spring-sown annual. Harvest the pods as they turn brown, before they split, and finish drying them in a paper bag. Ripe pods shatter and the plant self-seeds freely; in some regions, such as the western United States, it is listed as a weed, so remove the stems while the pods are still green unless you want a crop of volunteers next year.
Questions
Why is black mustard listed as Rhamphospermum nigrum?
It is the currently accepted botanical name; most seed catalogues and books still use the older name Brassica nigra.
How is black mustard used in Indian cooking?
Cooks fry the whole seeds briefly in hot fat until they crackle, then add them to dals, sambars and pickles.
Will black mustard self-seed?
Readily. Ripe pods split and drop seed, so harvest or cut the stalks before the pods dry.