CO-Horts Blog

Wednesday, November 2, 2022

Deadly Plants: The Castor Bean

 Posted by: Alison O'Connor, Larimer County Extension

Castor bean (Ricinus communis) is a tropical beauty native to east Africa that is extremely showy, but also incredibly poisonous. It’s commonly planted in the landscape as an annual to provide structure, color, and texture. I first met castor bean during a family vacation in northern Minnesota as a young teenager – more on this later.

Castor bean leaves and seedpods

In frost-free climates, this semi-woody plant can grow up to 40 feet tall, but in Colorado, you can expect annual growth of up to 10 feet. It won’t survive temperatures below 32 degrees. It’s an absolute garden showstopper with vibrant red, pink, or green seedpods that are spikey and persistent in late summer. Leaves are star-shaped and up to 18 inches across on long petioles. The Latin Ricinus translates to “tick”, as the seedpods are said to resemble blood-filled ticks. The seeds are small and look a little like black-eyed peas.

Large, showy leaves of the castor bean (no, it's not THAT plant)

The plant is in the Euphorbiaceae family (think poinsettias and spurge), so there will be milky sap with any broken plant part. Those with allergies to latex may have reactions to the sap, so wash your hands and wear gloves when handling the plant.

But the sap really is a minor issue when it comes to poisonous nature of this plant. The seeds are filled with ricin, one of the world’s deadliest natural poisons, a blood-coagulating protein. Ricin is an estimated 6,000 times more poisonous than cyanide!

Castor bean seeds [photo from]

Back to northern Minnesota…

My brother was a budding horticulturalist (and still is!) and he came across this plant during our trip. Some kids collect rocks, but Jeffrey collected plant parts and seeds. Not knowing what it was, he picked off a few of the seeds, put them in a black plastic film canister (remember those?!), and brought them home.

We had a beagle mix named Bosley growing up. He was a great dog but an absolute food hound. What Bosley consumed was legendary – entire loaves of bread, charcoal from the grill, two pounds of Starlite mints, mouse traps baited with peanut butter, an entire jar of peanuts – he ate anything and everything. He was a counter surfer and was known to steal boiling hot French fries off the oven tray.

Sweet Bosley - look at that face! His obsession for food was legendary.

A few months after our trip “up north”, the film canister was knocked off Jeffrey’s dresser, ended up on the floor, and sweet hungry Bosley ate some of the seeds. And he got really, really sick. Our family vet, Dr. Fred, suspected that he ingested something poisonous and eventually we figured out the puzzle, but only after we had the seeds identified. None of us realized how poisonous the seeds were (4-8 seeds can kill an adult human). Boz was in tough shape in ICU and we were all nervous wrecks.

Fortunately, with the help of the University of Minnesota Veterinary Medical Center and their toxicology lab, Bosley survived. His legend lives on since Dr. Fred wrote up a scientific publication about his treatment for him – Boz has a refereed publication! I remember picking up Bosley from the vet. He was a bit sluggish and a little worse for wear but recovered in time…and continued his quest to eat anything and everything his entire life. Fortunately, there are now antidotes available for any accidental poisonings that occur.

Interestingly, the poison ricin is being investigated as an anti-cancer agent – another common name for castor bean is “Palm of Christ”. And maybe you took castor oil to help you with heart burn or constipation? Don’t worry about being poisoned. Ricin is water soluble and is not released during the pressing process.

Castor bean really is beautiful!

The plant grows easily from seed (just limit how many you purchase online to avoid the watching eyes of the FBI) and needs regular water in the summer. But just heed caution when it flowers and produces seed. If you have young kids or hungry dogs in the landscape, it’s best to admire it in photos instead.

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