Another Garden Thug—Castorbean

I have observed recently that certain plants bring a mix of good and bad traits to the garden. In some cases, a plant’s positive characteristics can offset the negative ones. As a result, the gardener might want to include the plant in this landscape and accept the reality that it will require “special handling.”

One such plant is the castorbean (Ricinus communis), also known as the castor oil plant. This is a member of the spurge family (Euphorbiaceae), native to the southeastern Mediterranean Basin, Eastern Africa, and India. It grows as a large shrub that can attain a height exceeding thirty feet. The popular garden varieties, however, grow to ten feet or less.

The plant has several positive qualities, foremost being the striking appearance of its leaves, which are palm-shaped (palmate) and dark reddish-purple in color, becoming green with age. The shrub grows fairly quickly, and the gardener can control its shape with regular pruning. Also, being native to a Mediterranean climate, the castorbean, once established, is drought tolerant in the Monterey Bay area.

Castorbean leaves & seeds

Castorbean seeds, leaves and flowers

Another positive quality is the plant’s usefulness for medicinal, insecticidal, and industrial purposes. There are several medicinal uses, including as a laxative. The greatest commercial value of the beans (actually seeds) is for motor lubrication. These applications do not, however, contribute to its value in the garden.

The negative qualities must be acknowledged. First, the raw seeds are extremely toxic when chewed. They have been described as the most poisonous in the world. The seeds can be attractive and tasty-looking, but as few as four-to-eight seeds can be fatal to an adult. If you have this plant in your garden, you should ensure that neither children nor pets have opportunities to sample the seeds.

The plant is also strongly allergenic. Its pollen can trigger asthmatic attacks, and its sap can cause skin rashes.

Another negative quality is the castorbean’s tendency to propagate itself by dropping seeds. My plant has generated several crops of seedlings within a circle about thirty feet in diameter, centered on the mother plant. How the seeds plant themselves well beyond the plant’s drip line remains a mystery. The seedlings grow quickly up to three feet in height, but are easily uprooted. They do not transplant well, so I have not potted them for other gardeners. They might have inspired mixed reactions, especially by gardeners with children or pets.

Despite its toxicity and allergenic potential, the castorbean is grown for its ornamental value throughout the world in compatible climates. This reality demonstrates the appreciation of avid gardeners for plants that bring unique contributions to the landscape.

For at least some gardeners, the castorbean’s reddish-purple leaves are more important than the effort involved in protecting against the plant’s poisons and eradicating its unwanted progeny.

Each gardener must make such decisions for his or her own garden.

One thought on “Another Garden Thug—Castorbean

  1. Good pointers regarding the castor bean! An interesting specimen plant, unusual enough for even non-gardening types to notice, but with some of the bad habits you outlined. I had the same experience you did after planting castor beans from seed. I bought them way-back-when from a catalog, they performed beautifully, grew very quickly and were definitely showy. The “volunteers” were easy to pull and, as you mentioned, came up everywhere within a 30’ radius from the parent plant. As a conversation piece, it was hard to beat and seemed perfectly adapted to this climate. I’ve seen hundreds of plants advertised as problem solvers or dramatic eye-catchers with no mention of the fact that have terrible personal problems. Much like a really bad internet dating site. If someone sells you a tree that will break out the sides of your neighbor’s pool while looking for water, you might want to have that information first!

    Thanks!

    Steve

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