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?
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.
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 has an NPK of about 4-2-1 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.”
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.
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.
I live in Illinois and I plant castor beans and this year they came back up in the spring on their own.