The Striking Castor Bean

Of the many plants in my garden, one that I particularly appreciate is the Castor Bean, because of its several interesting characteristics.

This plant, known botanically as Ricinus communis, is a member of the very large Spurge family (Euphorbiaceae). It grows as a tree that can exceed thirty feet in height in nature, but generally reaches only about ten feet high in gardens. It is native to the Mediterranean Basin, East Africa, and India, and has become widespread in tropical regions. It is widely grown in southern California gardens, and it also grows well in the Monterey Bay area.

The form and color of its leaves are its most striking characteristics. While there is considerable variation in the leaf color, the most common variety begins with dark green and develops into a dark and glossy reddish-purple. This color can provide a dramatic ornamental value to the landscape.

The leaves are palmate, i.e., shaped like a maple leaf, but with five to twelve deep lobes with coarsely toothed segments. From August to November, it produces both male and female greenish-yellow flowers that lack petals. The female flowers have red stigmas, producing a showy appearance. The flowers are followed by an abundance of reddish-brown seed capsules.

Castor bean leaves and seeds

All parts of the plant are poisonous, and the seeds are strongly poisonous. They contain the highly toxic substance, ricin, which has become notorious in connection with international terrorist actions.

Castor oil can be extracted from the seeds, and with proper care can be made poison-free. The oil has several medicinal applications, including as an unpleasant purgative, which was more popular in my youth than it is today. The oil also has commercial applications, e.g., in hydraulic brake fluids, laundry detergents, and paints and varnishes.

In the garden, this poisonous plant must be managed with care, particularly if young persons are present on occasion. While children are unlikely to nibble the leaves, twigs, or flowers of any plant, they might find the seeds of the castor bean to be appealing. One seed could kill a small child! Certainly, children should be educated to enjoy but not eat plants in the garden, unless specifically invited.

Gardeners likely to have children roaming about in the garden unattended might well decide that plants other than the castor bean could provide an interesting feature in the landscape. 

Another characteristic of this plant is its vigorous growth habit. It has created more rapidly growing seedlings than any other plant in my garden. It would not take long to have many castor beans in one’s landscape.  In fact, it is considered an invasive plant anywhere in California. Its invasiveness is based more on its enthusiastic spread than a capability to out-compete other plants.

Recently, when I pruned back some branches that were encroaching on a walkway, the work caused several seeds to drop, and they soon sprouted to create a carpet of seedlings.

I have found the castor bean plant to be fairly manageable, because the seedlings, although many in number, are readily recognizable and easily pulled. The seedlings are probably easy to transplant, but I have not potted up any to share at the local garden exchange because of their combination of prolific propagation and poisonousness.

Many garden plants are well behaved and uniquely attractive, but others stand out in one way or another. The castor bean is an exceptional performer through its gorgeous leaf color, vigorous self-propagation, and the deserved reputation as the world’s most poisonous plant. If you can handle it, you too might enjoy having this plant in your garden. (Let me know if you’d like a seedling!)