Ricinus communis Seeds | Castor Bean

Spiny red seed capsules and huge bronze palmate leaves of castor bean — Castor Bean (*Ricinus communis*): Euphorbiaceae, north-eastern Africa, naturalised throughout the tropics.

LATIN NAME: Ricinus communis

COMMON NAME: Castor Bean

Plant Profile

Castor bean is not a bean and not a bamboo, though it is often described as both: it is a fast-growing, soft-stemmed shrub or small tree of two to four metres, with huge, glossy, palmate leaves in green, red or bronze and spikes of monoecious flowers. The seed capsules are spiny and round, and the seeds inside are mottled and beautiful, and among the most toxic seeds in the plant kingdom. It is native to north-eastern Africa and has naturalised across the tropics. In a single season from seed it can make a plant the size of a small tree, and then the first frost ends it.

Science & Biotechnology

The seed contains ricin, a type II ribosome-inactivating protein of extraordinary potency: a few chewed seeds can kill a child, and the purified toxin is a controlled substance under international conventions. The oil, by contrast, is safe once pressed, because ricin stays in the meal, and castor oil has been a laxative and an industrial lubricant for centuries, prized for its viscosity and its resistance to freezing. The plant is also a source of the allergen responsible for castor dust asthma, which is an industrial hazard rather than a garden one. Its seed coat is impermeable until it is nicked, which is why soaked seed germinates so much faster. Its seed is also the source of a commercial polysaccharide used in drilling muds and in paper.

Uses & Benefits

Castor oil is the industrial product: a lubricant for engines and plastics, a component of paints, soaps and hydraulic fluid, and a feedstock for sebacic acid. In the garden the plant is grown purely for its architecture, a bold tropical foliage plant for a bedding scheme or a large pot, and it is one of the fastest ways to fill space in a single season. It has no culinary use and no place near children or livestock, and the seed must never be tasted. The pressed meal is used as fertiliser only after the toxin has been destroyed by heat, which is an industrial process, not a kitchen one. The hollow stems are sometimes used as canes in vegetable gardens, though they are brittle.

Growing from Seed

Soak the seed for a day, then sow two centimetres deep in a free-draining mix at twenty to twenty-five degrees; germination is fast, often within two weeks. Grow the seedling in full sun and rich, moist soil, and plant out after the last frost, since it is killed by frost. In a short season it will still reach two metres. Wear gloves when handling the seed, keep the packet labelled and out of reach, and remove the seed heads before they shatter if children use the garden. It also makes a fine large pot plant for a patio.

Our Take

A magnificent and genuinely dangerous plant, grown for its leaves and handled as though the seed were what it is. Admire it, label it, and keep it away from anyone who might taste it.

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