Castor Beans – Are They Poisonous?

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Robert Pavlis

I was giving a talk at a local Master Gardner meeting the other day and I mentioned that castor beans contain one of the world’s most deadly organic compounds. Someone in the audience commented that you can actually eat several castor beans and you would only get a mild stomach ache.

These two points of view seem to contradict one another. What is the real story?

Castor beans, caster bean plant, Ricinus communis
Castor beans, Ricinus communis

 Deadly Castor Bean

The castor bean plant, Ricinus communis, is a native of tropical Africa and is grown in many gardens in North America for its fabulous large leaves. Here in zone 5 it is an annual that can grow to 5 feet in one season.

The castor bean plant itself is not poisonous to humans, but the seeds are. The seeds contain a protein called ricin and there is no question that ricin is very poisonous to humans, animals and even insects.

The castor bean holds the Guinness Book of World Records title for the world’s most poisonous plant, due to Ricin. Several lists of the poisonous chemicals exist on the internet and ricin is in the top ten list most of the time. Its position on any given list depends on how the list is defined. Does the list look at all chemicals or just naturally occurring ones? Is it looking at the castor bean or pure ricin? The details are not important; but the conclusion is clear – ricin is one of the most deadly naturally occurring chemicals. It is also more deadly than most man-made chemicals.

Compost Science for Gardeners by Robert Pavlis

It is reported that as few as 5 beans is enough to kill an adult human. Fewer beans will kill a child.

Are the Castor Beans Really Poisonous?

Would it surprise you that you can eat a handful of beans and have no effect from them?

The skin of the bean is quite firm and thick. If you swallow the castor bean whole, it will travel through your system intact. No ricin will enter your body. To release the ricin into your system you must chew the beans before swallowing them.

So I guess you could argue that the beans are not really poisonous so long as you don’t chew them. It then follows  that you will not be poisoned by just handling the beans–a common gardening myth.

 Is Castor Bean Oil Poisonous?

The oil extracted from castor beans does not contain ricin and therefore is not poisonous.

Should You Grow this Plant?

The plant itself is not very toxic so there is no reason not to grow it. If you are concerned about the beans, or you have small children, don’t let it make seeds. Remove the flowers as soon as you see them. In zone 5 they don’t flower until late fall.

Can a Castor Bean be Used to Murder Someone?

The actual bean is probably not a good weapon, but poisoning by ricin has been documented. For some interesting reading have a look at the death of Georgi Ivanov Markov – sounds like it would make a good movie.

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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!

21 thoughts on “Castor Beans – Are They Poisonous?”

  1. So- it’s safe to spray vegetables and the soil around them with a castor oil solution? I’m trying my best to keep groundhogs and voles at bay!

  2. How about cats? I’ve grown these before and cut the seeds off before they pop so the plants don’t spread. But if I miss some could it hurt cats scratching in the mulch and finding a seed?


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