Although the castor bean plant is considered a weed in many of the world’s tropical regions, the plant is cultivated in temperate regions, not only for its seed oil but also for its beauty as an accent plant in the garden. Castor bean is native to parts of Africa and India and has been used in these areas for cosmetic, healing, and household purposes since ancient times.
Seeds of the plant have been found in 4,000-year-old Egyptian tombs. The Ebers Papyrus, an Egyptian medical text dating to ca. 1550 BCE, specified that the oil was useful as a laxative. In the Middle Ages, European herbalists used the herb as a liniment.
The seeds, commonly called beans, contain up to 5 percent of the protein ricin, which is one of the most toxic natural poisons. The extraction process used to produce oil from the beans removes the poisonous compound.
Common Names: Castor Bean, Mole Plant
Description: Shrub, 8 to 10 feet tall, with alternate, palmate leaves up to 2 feet across, gray-green or dark purple-red; flower clusters on terminal spikes; spiny, 1-inch fruit capsules with seeds (beans)
Hardiness: To Zone 8
Parts Used: Seed
Range/Habitat: Native to tropical Africa and East Indies, naturalized throughout the tropics
In addition to its use as a mild laxative, commercially produced castor bean oil can be applied topically as a skin moisturizer and to treat skin inflammations and warts.
Caution: Castor bean oil (also called castor oil) is not recommended for pregnant and nursing women and young children. The beans should never be taken internally in any form; the body can absorb the ricin in the seeds and the result can be severe poisoning and death.
Fast-growing castor bean is a popular foundation plant for new homes in southern regions. The plant’s height and large, showy leaves also make a dramatic backdrop for lower-growing ornamentals in mixed borders. Planted in a large container, castor bean gives decks, porches, and verandas a lush, tropical look.
Sometimes called “mole plant,” castor bean reputedly deters rodents and rabbits, so some gardeners plant a castor bean hedge around their vegetable garden to repel animal pests. It is said that if you put a few seeds in a mole’s hole, the little animals will move elsewhere. Certain ecofriendly mole repellents have castor oil as a major ingredient.
Researchers at Michigan State University found that a commercial mole repellent containing 65 percent castor oil was effective for a period of 1 to 2 months. The bean’s toxicity is probably a mechanism that evolved to ward off insect and pest attacks. It has been studied as a potential insecticide, but this would seem to be very toxic to humans and animals, as well.
How to grow it
Plant castor bean seeds 1 inch deep in fertile, well-drained soil and full sun. In Zone 7 and colder, grow castor bean as an annual. Start the seeds indoors about 1 month before the last spring frost date, then transplant the seedlings outdoors after all danger of frost has passed. Keep plants well watered and away from young children and pets. Harvesting the plant for medicinal use is not recommended.
Castor Oil and Early Flying Machines
The goggles and scarf were not just a fashion statement; they were an essential part of flying. The design of the rotary engine that powered many of these planes — the fact that it spewed lubricating oil into the air during flight — caused the pilot’s face and parts of his body to be covered with the spray.
Castor oil was the best lubricant for this type of engine, which meant that pilots ingested a great deal of it during each hour of flight. And because castor oil is a purgative, this had an immediate effect on the pilot’s intestinal system, resulting in the need to run to the facilities after every flight. Thus, the long, protective silk scarf wrapped in many layers around the pilot’s nose and mouth became a mandatory part of flying gear.
In later years, closed cockpits and other types of engines eliminated the need for the scarf, but the style was set. Today, there are still some high-performance motor lubricants that contain oil extracted from the castor bean.