Ricinus communis Seeds | Castor Bean
LATIN NAME: Ricinus communis
COMMON NAME: Castor Bean
Plant Profile
Castor bean is grown as a foliage plant in temperate gardens and as an industrial crop in the tropics, and the same species does both jobs without modification. Ricinus communis is a fast, soft-wooded plant that can reach 3 m in a single season in warm conditions, carrying large, deeply lobed leaves up to 60 cm across on hollow stems that are often flushed with red or purple.
The flowers are unremarkable, but the seed pods are not: they are spiny, waxy and brightly coloured, ripening from green to red to brown before they split explosively and throw the beans a metre or more. Each bean is mottled grey and brown like a tick, and it contains one of the most toxic proteins known.
Science & Biotechnology
Ricin is a type 2 ribosome-inactivating protein: one chain binds to cell-surface glycoproteins, the other enters the cell and shuts down protein synthesis by removing a specific adenine from the ribosomal RNA. By weight it is among the most toxic naturally occurring substances, and a small number of chewed seeds can be fatal, which is why castor bean is one of the few garden plants with a genuine safety literature rather than an imagined one.
The industrial interest is the oil, not the toxin. Castor oil is 85-90 per cent ricinoleic acid, an unusual hydroxylated fatty acid that gives the oil a viscosity and a stability almost unmatched among vegetable oils. It goes into lubricants that must work at high temperature, into polyurethane and nylon intermediates, and into cosmetics. The toxin stays in the pressed meal, which is why castor meal is used as fertilizer only after detoxification and never as feed without processing.
Uses & Benefits
In the garden the plant is used for tropical effect: a single specimen in a border gives the scale of a banana or an aralia, and the dark-leaved cultivars such as ‘Carmencita’ are among the few plants that supply near-black foliage at 2 m. It grows fast enough to work as a summer annual even in a short season.
Medicinally, castor oil is a stimulant laxative with a long record, and its use as a poultice is traditional in both European and Ayurvedic practice. Both uses should be treated with respect rather than enthusiasm. The oil sold for medicinal or cosmetic use is refined and safe; the beans are not, and the difference between them is the whole point.
Growing from Seed
Sow castor seed indoors in early spring at 20-25°C, 2-3 cm deep in a free-draining mix. Germination takes ten to twenty-one days and is usually reliable. The seedlings grow quickly and need a deep pot, since the taproot develops fast and resents being cramped.
Plant out only when the soil is properly warm and all risk of frost has passed; cold checks the plant badly and it may never recover its momentum. Give it full sun and plenty of water in dry spells, and stake it in exposed positions, because the stems are hollow and the leaves catch wind. Wear gloves when handling seed and wash hands afterwards; keep the seed away from children and pets, and remove pods before they split if you garden where they might be found.
Our Take
Grow it if you have the space and the sun, and handle the seed as you would any toxic material. The plant pays you back in scale and speed, and nothing else in a temperate garden produces that tropical silhouette in one season.
Related Reading
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