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Native to Africa, the castor bean is a dramatic tropical plant featuring leaves as big as dinner plates and attractive seedpods. It can easily grow 10 feet (more for some varieties) in a single season; the height makes an eye-catching backdrop in the garden and adds intrigue to bland borders. In most zones castor bean is an annual; in frost-free climates it can become a small tree. Every part of this plant is poisonous if ingested, so plant with caution.
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Castor bean features reddish-brown seed capsules and large, glossy green leaves with five to 11 deep-toothed lobes. Some varieties sport attractive bronze or burgundy foliage. Given the showy nature of its other aspects, the fact that castor bean has small, dull flowers may come as a surprise. Spikes of small cup-shape greenish-yellow flowers appear June to October. Each female flower sports a red stigma, the sticky bulb seen in the center of the petals. Pollen lands here and begins the fertilization process. The seedpods emerge as bright red or pink then dry to a dull brown before splitting open to reveal highly poisonous seeds.
Deadly Castor Beans
Castor bean is extremely poisonous due to the deadly compound ricin in all parts of the plant, but especially the seeds. The seeds are safe to handle because they have a protective coating.) However, the seeds do contain nontoxic oil harvested for numerous uses, including industrial, cosmetic, and as a laxative. If you can't resist adding this tropical plant to your landscape, consider cutting off flower stalks before they mature to prevent them from setting seeds. Two more warnings: The sap may cause skin sensitivity, and the pollen of the blooms is highly allergenic.
Castor Bean Care Must-Knows
Castor bean thrives in rich, evenly moist, well-drained soil. It can handle part shade, but it needs full sun to achieve the best height and flowering. Keep in mind the plant can reach 6 to10 feet in a single growing season, which means it needs support when grown in part shade to avoid flopping or snapping in strong winds. Castor is drought-tolerant once established. In tropical climates, it becomes weedy and spreads aggressively if given the chance.