Castor Bean Plants

Castor bean plant up-close
David Beaulieu

Some plants, while they have roles to play in your landscaping, are hardly conversation pieces. For example, catmint can be a nice ground cover, but rarely will a visitor walk onto someone's landscape and remark, "Wow, look at that catmint!" It is not designed to evoke such a response; rather, its purpose is to play a supporting role. Castor bean plants, on the other hand, have star power.

What gives Ricinus communis (which is the botanical name) its star power? Let's consider the three T's: tall, toxic, and tropical. It is because castor beans possess these three qualities (and more) that they are such interesting plants.

Tall, Dark, and Handsome?

Grown during the summer in a Northern landscape, these fast-growers will typically reach a height of 6-10 feet (occasionally becoming as tall as 15 feet when started early in a greenhouse and provided with ideal conditions). If you grow several of them, this trait can make them useful as living privacy fences for the summertime. 

But its height is just one attribute that makes castor bean stand out in your landscape. The coarsely-textured leaves furnish fodder for spectacular textural contrasts with plants that have smaller leaves. Even the green-leaved types attract attention because the leaves are star-shaped. If that's not enough for you, some cultivars offer dark foliage. On others, such as the Ricinus communis 'Carmencita' in the image above, the young leaves can start out reddish if given sufficient sunlight. As you can also see from my photo, the stalk can be a bright red color.

While the flowers are insignificant, the red seed capsules covered in spines do possess ornamental value. When these pods dry, they explode, turning the seeds that had been trapped within into projectiles. Even the seeds, themselves are attractive, sporting an endless number of color patterns.

It is perhaps the appearance of these seeds that gives the plant its genus name, Ricinus, which translates as "tick" in Latin (there is also an unrelated perennial named "tickseed"). Unfortunately, the literature on the subject can't seem to decide whether the plant was named after the tick or vice versa. Regardless of the confusion surrounding the origin of the botanical name, castor bean plants merit specimen status, possessing some ornamental traits for which other plants would kill.

Toxic Terror, Care

poisonous plant in all its parts, castor bean's namesake "beans" (i.e., the seeds) are especially toxic. They are the source of the infamous poison, ricin. If you've followed the news much at all in this crazy 21st century in which we live, you probably remember encountering at some point a report that went something like this: "Ricin-Laced Letter Sent to U.S. Senator." It's not often that a landscape plant makes it so big in the news, but, then again, our tall, toxic, and tropical star has a way of garnering the limelight.

Does the danger posed by castor bean plants frighten you? Their toxicity might be problematic if you have young children. If you're still determined to grow them, then lessen the danger by cutting off the flowers and disposing of them, thereby preventing seed formation.

The first step in good plant care is selecting an ideal location for your specimen and improving the soil (if needed) in that spot. Grow castor beans in an area with full sun and good drainage. If you doubt the soil's fertility, work some compost into the ground. Keep the soil adequately watered all summer.

Since castor beans are tall, slim plants with large leaves that act like sails in the wind, be sure to stake them unless you've located them in a spot sheltered from high winds.

Tropical Pizazz, Familiar and Surprising Uses

Many people are familiar with the fact that castor oil, an old-time laxative and purgative, is pressed from castor bean seeds. But did you have any idea that it is an ingredient in Castrol motor oil, a product that owes its very name to castor oil? That's just one of many benefits from this plant that most people would find surprising. Some gardeners, at least, are aware that castor beans are used in companion planting to serve as mole repellents.

Castor beans are not true beans; that's just a nickname. The plants belong to the Euphorbiaceae family. That makes them relatives of poinsettia plants and wood spurge. Tropical plants such as castor beans have a certain cachet in the Northern landscape, where they offer an exotic look. Hailing from Africa, Ricinus communis has naturalized in many other warm areas of the world. How warm? It is suited to growing zones 9-11, where it is classified as an herbaceous perennial. But in the North, it's pampered like the star that it is and only works summers, as if it were an annual.