Castor oil “beans” aren’t beans; they’re seeds of the castor plant, Ricinus communis. Easily grown, castor is propagated only by seed. Some think these tough, pest-defiant perennials grow too easily: Self-sowing plants sprout all over their property all summer. Among the world’s fastest growing plants, castor can attain heights of up to 40 feet tall and grow as much as 8 to 15 feet its first season. The tropical native is hardy in USDA Zones 8-11, likes temperatures between 60-85 degrees and are killed by frost.
Harvesting Castor Seeds
Wear sturdy canvas or leather gloves to harvest castor seed pods. The plant's fluids are toxic and the seed pods are heavily armed with rigid, closely set spines. The seed pods, spherical green, red, maroon or purple fruits about the size of large gumballs, are produced in early summer. They are ready to pick after they have turned completely brown in the period from late summer through early October.
Use garden shears to cut the pod cluster from the stalk. Remove and discard other fruit clusters from the castor plant to reduce the number of “volunteers" (wild seedlings) next year. These plants reseed prolifically and they’re self-pollinating, so you don't need many pod clusters.
Put 3 to 4 seed pods in an empty mesh onion bag and use a wire tie or string to close. Set the bag of pods in the sun to dry, making sure plenty of space exists between the pods for good air circulation. Keep dry; bring indoors when rain is forecast. When ready, each pod will split into three spiny sections, or carpels. Those will split and eject a single seed with quite a bit of force, potentially up to several yards away. Seeds are about the size of a pinto bean--shiny, tan or cream colored and beautifully marked with dark brown speckles.
Store the seeds in a brown paper bag in a cool, dark, dry location for up to two years. Plant them as soon as it’s practical, since the fresher they are the higher the successful germination rate will be.
Planting Castor Seeds
Prepare a 2-foot square planting site, after all danger of frost has passed, in a well-draining location that receives full sun. Work two to three spadefuls of organic compost into the top 2 feet of soil. Castor plants are deep, heavy feeders and love rich soil.
Soak castor seeds in water for about 24 hours prior to planting. The seeds are encased in a hard coating, and soaking will soften them.
Plant a seed 1 inch deep. For a thicker, more tropical display when castor plants mature, group 2 to 4 seeds spaced about 12 inches apart. These plants usually have a single main stalk with no branching, but large deeply lobed star-shaped leaves on long stems. For normal growth patterns, allow 3 feet between individual castor seeds or groups of seeds.
Water enough to keep the top inch of soil evenly moist, but not soggy, and don’t allow it to dry. Once established, castor requires less water and becomes increasingly drought tolerant with growth.
Apply a 1-inch layer of organic mulch when the castor seedling is 3 to 4 inches tall. Add another inch when the plant is 10 to 12 inches tall. This will help the soil retain moisture and keep the area relatively weed free.
Feed monthly with an all-purpose fertilizer beginning in late spring. Stop fertilizing in mid-November.
Apply an additional 2 inches of mulch in late fall, and extend it outward, roughly equal to the plant’s canopy. Water first-year castor plants during the winter only if an extended unseasonably dry spell strikes. Otherwise, normal rainfall will suffice.