Are Castor Bean Plants Poisonous – Should Gardeners Grow Them?

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Robert Pavlis

Cold climate gardeners are always looking for something exotic to grow and there are few plants that beat the dark red-leafed castor bean. Unfortunately, this plant has a bad reputation for being poisonous. Many experts tell you not to grow castor beans because they are so toxic.

I used to grow it, and grew a new variety last year. I am still alive! So how toxic is it? Is it safe to grow in the garden?

Are Caster Bean Plants Poisonous - Should Gardeners Grow Them?
Are Castor Bean Plants Poisonous – Should Gardeners Grow Them? Credit: Home of miniclover

What Is The Castor Bean Plant?

The botanical name of the castor bean or castor oil plant is Ricinus communis. It is a perennial in the Euphorbia Family (spurge) which are known to contain latex-like sap but the sap of the castor bean is more water-like. This is not a bean but the seed looks a lot like dried beans. The seed is the source of castor oil which is rich in triglycerides and contains the water-soluble toxin ricin.

Castor beans have been found in ancient Egyptian tombs dating back to 4000 B.C. and the oil was used thousands of years ago in wick lamps for lighting.” Today the oil is used in many products including Castrol-R racing motor oil, chocolate and cosmetics, particularly lipstick.

Microbe Science for Gardeners Book, by Robert Pavlis

The attraction for the gardener is that it grows quite tall in a short period of time and produces very large leaves. Plants started indoors reached a height of 7 feet by fall in my zone 5 garden. They can’t take frost. In warmer areas it establishes itself easily and can become invasive. It is a common weed in the southern US and in many tropical locations.

Why Is Castor Oil Not Toxic?

Castor oil is produced by cold pressing the seeds followed by heat. Since ricin is water soluble, the oil contains very small amounts and heating ensures it is removed. Almost all of the ricin remains in the leftover dried castor bean cake.

Castor bean cake can be used as a fertilizer or animal feed. The fertilizer usually as an NPK of 4-0.5-0.8 and includes several micronutrients. It may contain ricin and should be kept away from animals. The ricin is removed for feed products.

How Toxic Is The Castor Bean Plant?

The American Association of Poison Control Centers, recorded 110 calls about “exposure to castor beans” in 2010, but that there were “no major effects” reported as a result of those exposures.

The poison in castor seeds is a protein called ricin (RYE-sin), which is one of the deadliest natural poisons. It is 6,000 times more poisonous than cyanide and 12,000 times more poisonous than rattlesnake venom. One millionth of an ounce (0.035 milligram, or 4 seeds) can kill an adult male.

Apparently, you can swallow the seeds and they won’t harm you, unless you chew them well. The outer coating on the seed is not toxic.

The plant itself is not toxic either. “Unintentional exposure to ricin is highly unlikely, except through the ingestion of castor beans.”

Castor bean seeds
Castor bean seeds

Are Seedlings Toxic?

The seeds contain ricin but what about the seedlings?

The ricin in the seed is mostly contained in the endosperm, the stored food for the seedling. The cotyledons in the seed may also have some. As the shoot grows, ricin is converted into non-toxic compounds. Four days after planting only 50% remains and it drops more quickly after that. Seedlings that were 10 days old had no ricin.

Seedlings are safe to handle, but it is probably not a good idea to eat them as sprouts.

Do Castor Beans Repel Moles?

Apparently Thomas Jefferson planted castor beans in the hope that they would deter moles. It is unlikely that the plant deters moles but there is a castor bean extract called Mole-Relief™ that claims to repel them but to date products based on castor bean oil have not been very effective for repelling moles.

Synthetic vs Natural Chemicals

So many people are afraid of synthetic chemicals and there certainly are some to be concerned about. When I’m giving a talk on this topic I use the caser bean as an example of a natural organic chemical that is more toxic than just about every synthetic one.

Synthetic and natural chemicals can be safe or toxic. Each chemical needs to be evaluated and understood on its own merits.

Castor bean in my garden
Castor bean in my garden

Should You Grow Castor Beans

In cold climates castor beans do not produce flowers or seeds until late summer or fall. If you are concerned about them, just cut off the flowers. The seeds are also produced very high on the plant. There is no way a child or animal (except bears) could reach them. The plant itself is not toxic.

I see no reason why you would not grow this plant, provided you are willing to start it inside each year.

In warm climates the plant can be invasive and may already grow wild where you live. In that case it is important to educate children about the seeds and remove them when you see them, both because they are toxic and they are invasive.

If you do grow this plant, try one of the red-leafed cultivars. It will make a great accent in the garden.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

16 thoughts on “Are Castor Bean Plants Poisonous – Should Gardeners Grow Them?”

  1. My Grandmother grew castor bean plants for decades. I have grown them too for many years. The seeds are high above any children and pets on the plant 4 to 5 feet tall in a casing. I have to soak the casings even to get the seeds out. Birds or animal have never been interested in these plants. I cut of these casings and burn them in the fall just to be safe. I grow them for their beauty in a fenced yard in a secluded area.

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  2. Hi from New Zealand, moved recently and lost 2 cats to kidney and general organ failure. Castor bean plants here are invasive and sucker like crazy, Can’t blame castor definitively but second cat had stuff that looked like castor sap on it and could have eaten some beans. Anyway scorched earth policy here for castor plants, also no feral cats here at all (Marlborough) and they are a problem everywhere else, so something toxic to cats in the environment. Thanks.

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  3. Fun fact: Because castor beans are the precursor for Ricin based nerve agents, large shipments of castor beans are monitored closely to ensure certain nation states and terror organizations don’t get a hold of large enough stockpiles to create a chemical weapons program.

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  4. Thank you for this fun and informative blog! Here in S. California they grow beautifully, and the bees love them. All the best to you!

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  5. It is not invasive here in zone 5 (midwest) BUT since birds fly AND some fly south, in the fall when seeds r ripening and they don’t respect state lines, I choose not to plant castor bean. If I lived north of California, I would reconsider. Lol

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  6. The red-foliage form is a beautiful plant and excellent as an annual that will get killed off by frost.

    Here it is classified as a noxious weed because of our frost-free climate. It becomes a gangly tree that will live for years and reseed lavishly.

    One advantage to a cold climate is that certain plants that are pests in warm climates are well-behaved annuals where winters are significant!

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  7. Thanks or clarifying the poison in castor bean plants. I have been growing them (Zone 5b) for several years. I usually have enough self-seeded plants starting the next spring that I can cull the small ones and grow the rest. They are not in an area with dogs or children. Passersby are always asking about these beautiful and unique plants.

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  8. I have always wanted to try these but never have because of the association with it. Now I will after reading your much more detailed explanation of it. The exotic looking leaves have made me want to try it in our pool area. Thanks.

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  9. Some of the most toxic plants in our gardens are ones we eat parts of: rhubarb, tomatoes and potatoes come to mind. Do we stop growing these because parts have toxins? So much silly advice out there. Thank-you for dispelling all these myths.

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  10. My mother grew Castor beans, nightshade, oleander, and datura in her garden in Arizona. Her yard was fenced, and she knew what she was doing with her plants, and her cat knew better than to eat flowers in the garden. I have to admit they were attractive; I imagine the fact that they were poisonous added a bit of interest to the garden. I imagine that if she’d have lived in the Middle Ages, she might have been thought to be a witch, what with her garden and her familiar.

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  11. All I have to say is I Love Castor Bean Plants in my garden! Just when I am wondering how your going to come up with yet another interesting topic, you hit us w castor beans. Love it! Your inspiration for finding new topics seems to know no end. Ty!

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  12. This brings back fond childhood memories of playing among the giant Castor Bean plants my mom grew around our house in Zone 9 Houston. We hid in them, broke the leaves off to use in imaginative ways and threw the pods at each other without any issue. Thanks for another interesting and informative myth busting post.

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