Culture
Winter hardy to USDA Zones 9-11 where plants will thrive in rich, evenly moist, well-drained loams in full sun. Plants tolerate part shade, but best height and flowering occur in full sun. Site in locations protected from strong winds. In Zones 9-11, sow seed directly in the garden at last spring frost date. Plants can become somewhat weedy and spread aggressively in frost-free areas. North of USDA Zone 9, plants may be grown as warm weather annuals by sowing seed indoors in pots about 6-8 weeks prior to last spring frost date. Plants may be grown directly in the soil or in large containers or tubs.
Noteworthy Characteristics
Ricinus communis, commonly called castor bean, is probably native to tropical Africa. It is an erect, rapid-growing tender perennial that is grown in St. Louis as a warm weather annual. In certain parts of the U.S., including Missouri, it has escaped gardens and naturalized in fields, waste areas and along roadsides. It will grow rapidly in a single season to 6-10’ tall. Ornamentally, it is most valued for its (1) huge, palmately lobed (5-11 pointed lobes), toothed, glossy green leaves (each to 1-3’ across) and (2) round, spiny, reddish-brown seed capsules. Small cup-shaped apetalous greenish-yellow flowers in spikes are not particularly showy. Each female flower has a red stigma. Every part of this plant is POISONOUS if ingested, particularly the seeds which contain highly toxic ricin. Oil from the seeds has been used in a wide variety of industrial applications. Castor oil can be extracted from the seeds and is not toxic. Plant cultivars, dwarf and large, are available, some having attractive reddish, bronze or purple leaves and some having bright and colorful flowers.
Genus name comes from the Latin word ricinus meaning a tick from the appearance of the seeds.
Specific epithet means common.
Problems
No serious insect or disease problems. Spider mites may appear. Do not plant this annual in areas where small children play. Seed capsules may be pinched off when small to remove poisonous seeds from the plant. Contact with plant foliage may cause allergic skin reactions in some individuals.
Uses
Shrubby annual. Specimen. Containers.