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In frost-free areas, castor bean is an evergreen herbaceous or semiwoody large shrub or small tree that gets up to 40 ft (12 m) tall and 15ft (4.6 m) wide. In the tropics, it can have a trunk that is woody near the base and up to a foot in diameter. Elsewhere, castor bean plant grows as an annual that can get 8-15 ft (2.4-4.6 m) tall in a single growing season. This is a fast growing, suckering, colony forming plant with decidedly tropical looking foliage. They tend to grow straight up at first, developing branches only later in the season (and in subsequent years for plants that live that long). The huge leaves are palmate, with 5-11 deeply incised lobes. They are glossy purplish or reddish-green and 12-30 in (30-76 cm) across, with long petioles (leaf stems). The stems are watery juicy and reddish or purplish too. The inflorescence is not particularly showy; small, 0.5 in (1 cm) wide greenish yellow flowers are borne in fat spikes 8-18" tall near the tops of the stems. Female flowers are on the top half of the spike and have conspicuous red stigmas (the parts that receive the pollen). The male flowers on the lower half of the spike have conspicuous yellow anthers (the parts that give off the pollen). The female flowers are followed by reddish brown egg-shaped capsules, about an inch long, thickly covered with soft flexible spines. Each capsule contains three seeds that look like fat swollen dog ticks and are deadly poisonous.
Location
Castor bean is very easy to grow; too easy, some might say. They have a tendency to self sow and new seedlings can pop up all summer long. This is one of the fastest growing plants in the world and becomes almost treelike in 3-4 months. It will need to be staked if grown where the wind can blow it over. Light: Full sun is best. Moisture: Castor bean grows fastest and largest with abundant water, but once it gets established, it can tolerate drought - it just won't grow as fast. Hardiness: USDA Zones 8 - 11. Castor bean is a big evergreen shrub or small tree in zones 10-11. It usually won't live through the winter, but can be expected to reseed itself in zones 8 and 9, and maybe in zone 7. Plants sometimes sprout back from the roots after freezing in zones 8B and 9. Castor bean is widely grown as an annual in cooler climates. The castor bean plant can tolerate a touch of frost. Propagation: Castor bean seeds germinate quickly, and the plants grow very fast. They can be expected to self sow under favorable conditions. Germination can be hastened if the seeds are soaked in water for 24 hours or nicked with a file before planting. Sow in place in zones 8-11. In areas with shorter growing seasons, or to get a head start, sow seeds indoors in individual containers 6-8 weeks before the last expected frost.
Usage
The castor bean seed coat contains ricin, one of the most poisonous naturally occurring chemicals known to Man; even very small doses can be fatal. Castor oil, derived from castor beans, is used extensively in medicine and in varnishes and paints, as a lubricant and lamp oil, and in many other industrial and manufacturing processes. The foul tasting laxative, castor oil, loathed by children everywhere, tastes poisonous but is, however, a valuable purgative still widely used in modern medicine. Castor oil also is used externally to treat some kinds of skin diseases including ringworms and warts. The genus name, Ricinus means "dog tick" in Latin, because that's what the seeds look like.
Steve Christman 8/2/00; updated 11/07/00, 2/7/03, 10/26/03, 4/24/04
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