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 pointed lobes like fingers on an open hand. 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. The seedpods emerge as bright red or pink then dry to a dull brown before splitting open to reveal highly poisonous seeds.
Related: Guide to Growing Tropical Plants
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.
More Varieties of Castor Bean
'Carmencita Bright Red' Castor Bean
As the name implies, this variety of Ricinus communis features maroon foliage and bright red seed pods. Zones 9-11
Castor Bean Companion Plants
Cannas bring tropical splendor to gardens in all regions. These bold plants feature clustered, flaglike blooms in a brilliant color array on tall stems. Recent flower breeding has created canna foliage that is even showier than the petals, with variegated leaf combinations of orange, yellow, and greens that glow in the summer sun. Dwarf cannas are also available for container gardening and other small spaces. Cannas are usually grown from tuberous roots but some newer varieties can also be raised from seed, with flowering guaranteed for the first year. Cannas provide architectural interest in summer borders and they also flourish along the damp margins of a pond. If you garden in a climate colder than Zone 9 (7 for the hardier types of cannas), you'll need to dig canna plants up and store them bareroot for the next season or overwinter potted specimens indoors. A destructive mottling virus has threatened canna stock in nurseries across the U.S., so be sure to buy your plants from a reputable source.
Huge, showy blooms are the hallmark of the hibiscus family, whether the flying saucers on hardy perennial hibiscus, the Hawaiian charmers of the tropical hibiscus, or the frilly-flowered Rose of Sharon that grows into a large shrub or small tree. Not only do hibiscus blooms boast an amazing array of colors, vastly widened through hybridizing, they also draw hummingbirds en masse. The newer, dark-leaf introductions are wonderful architectural fillers in container gardens. Cold-winter gardeners can grow the more tender types of hibiscus in containers and wheel them into the house when winter approaches. Prune back heavily to encourage blooms, and watch for aphids and whitefly, which are attracted to all forms of hibiscus. Learn about the perennial varieties of hibiscus.
Attract butterflies and have fun doing it with big, bold, beautiful Mexican sunflower. Plant it from seed directly in the ground and watch it soar. It can hit up to 5 feet in just weeks with big, lush foliage and smaller but still showy flowers in sunset colors that butterflies love. Put a cluster of these bodacious beauties in the back of the border to give it height and drama. Many of the taller types need staking to keep them upright. Plant them outdoors after all danger of frost has passed in a sunny spot with well-drained soil.