Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Castor beans have gotten a bad rap because they are the source of the poison ricin. The truth is that the beans have been used for thousands of years. The plants also add a tropical touch to your garden.
What are Castor Beans?
Castor beans (Ricinus communis) are not true beans. They are a member of the spurge family which includes poinsettias and euphorbias. They are called beans because the seeds resembles beans. The plants are tropical, native to eastern Africa, the eastern Mediterranean and India. They have spread to other tropical areas in the world. In fact they have become nuisances in some areas. They are hardy in zones 9 through 11.
The plants are large bushes/small trees, sometimes growing to 15 feet tall. In northern areas, they are grown as annuals, reaching 6 to 10 feet tall in a single growing season. They need full sun and well-drained soil. Castor bean plants have large, exotic looking leaves which sometimes start out red and turn to green as they mature. Newer cultivars have been bred so that the leaves stay red.
The plants have both male and female flowers so they are self-pollinating. The seeds are contained in fruit that is spiny and either green or red, depending on the cultivar. Each fruit has three chambers, each containing a seed. The seeds look like beans and have mottled colors of brown, gray, black, white and maroon. When the seeds are mature and ready to be dispersed, the fruits open and forcefully eject them.
How Poisonous are Castor Beans?
Only the beans are poisonous. They contain ricin which is one of the most poisonous substances known. It only takes consuming four or five beans to kill an adult. Even eating one or two beans can make you very, very ill. Symptoms of ricin poisoning include vomiting, bloody diarrhea, and convulsions. The symptoms can last for up to a week.
If you are growing castor beans and are concerned that children or pets may eat the beans, simply remove the flowers so that the plants do not develop seeds. The rest of the plant is not poisonous. Only the seeds.
Is Castor Oil Poisonous?
Castor oil is not poisonous. The ricin toxin is water-based, so when the beans are crushed to release their oil, the water-based ricin stays with the “cake” or leftover material. It does not mix in with the oil.
Castor oil has been known and used for thousands of years. It was originally burned in oil lamps to provide light. Castor beans have been found in Egyptian burials. Castor oil has also been used for centuries as a laxative.
Does Castrol Motor Oil Contain Castor Oil?
Castrol oil originally contained castor oil. It’s how it got its name! Castor oil is an excellent lubricant. It was used in small engines where petroleum oil was too viscus. With the invention of modern synthetic motors oils, Castrol replaced the original castor oil with the new synthetics. However, the company does offer a version of their motor oil with castor oil for vintage engines.
How to Grow Castor Beans
Castor beans are often grown as ornamental plants They are sometimes planted as a privacy hedge because of their size. Choose a location that gets full sun and has well-drained soil. Amend the soil with compost. These are large plants that require a lot of nutrients. If you are making a hedge with your castor beans, plant them at least 4 feet apart. Water well after they are planted. Once established, they are drought tolerant so they won’t require supplemental watering unless you experience an extended drought.
You should also stake your plants. Initially, they will grow a single stem. Their wide leaves act like sails, catching the wind and bending the plants over. Later in the season, they will develop their wide side branches which will act as stabilizers, preventing the wind from blowing the plants over. Until then, stakes will be needed to keep the plants upright.
How to Grow Castor Beans From Seed
Most gardeners start their beans from seed. Germination is very poor unless you give the seeds a little help. There are two ways to improve germination.
The first method is to soak them overnight before planting. This softens the tough outer shell, allowing water to penetrate and start the germination process. Remember, these seeds are highly poisonous, so you must be careful if you live with children and/or pets. I have cats so I use what I call the “cup & saucer” method. I fill a teacup with water and place whatever seeds I am pre-soaking in it. Then I place the matching saucer on top. This prevents my cats from drinking the water overnight while I am sleeping. Since I grow a lot of plants from seed and often am pre-soaking different seeds, I place the empty seed packet under the teacup, identifying what is soaking that cup.
When soaking my castor beans, I always wear gloves. After the beans have soaked overnight, I immediately wash the teacup they were soaking in in my dishwasher to make sure that any ricin that may have leached into the water from the seeds is removed from the cup.
You can also scarify the seeds. Using a coarse file, rub it once or twice across the seed coat. You don’t want to do it too hard or too deep because that could risk damaging the embryo inside. You want to just weaken the tough outer shell enough so that water can penetrate it and start the germination process. You can plant the scarified seeds immediately after you file them. There is no need to pre-soak them.
In zones 9 through 11, where the plants are perennial, after soaking or scarifying, you can plant the seeds directly in your garden in May. Plant them 1 inch deep and 8 to 11 inches apart. Germination should occur in 1 to 3 weeks. When the seedlings are 3 inches tall, you can thin them to 4 feet apart.
In colder zones, you will need to start your seeds indoors, 6 to 8 weeks before your last frost. Plant the seeds 1 inch deep in containers after you have pre-soaked or scarified them. Germination should occur in 1 to 3 weeks. You can transplant your seedlings into your garden after your last frost when the soil has warmed. In my zone 6 NJ garden, I transplant my seedlings at the end of May at the same time that I am seeding my cucurbits which also need warm soil. Plant your seedlings 4 feet apart.
Questions & Answers
Question: How far apart should the rows be? I know in tow you said 4 feet apart but what is the distance between rows?
Answer: Castor bean plants are very wide in addition to being very tall. I would plant them in 4 feet apart in rows that are at least 4 feet apart.
Question: My neighbor gave me a castor bean plant to transplant. It was 3 feet tall. It’s drooping badly. Should it be cut down?
Answer: You don't say where you live so I'm going to have to guess what is wrong with your castor bean plant. Castor beans are tropical plants. They are only hardy (perennial) in US growing zones 9 - 11. If you live north of zone 9, then your plant is dying of the cold. North of zone 9, castor beans are grown as annuals. They cannot survive the winter. If you live in a tropical area (zones 9 -11), then your plant probably needs water. Once they are established, they are drought tolerant but if there has been no rain for weeks, then you need to give it some water to tide it over until the next rain.
Question: Can I plant castor beans in the same pot as tomatoes plants?
Answer: No, both are enormous plants and wouldn't fit in the same container. They should be grown in separate pots.
Question: Is it advisable to intercrop castor bean with tomatoes?
Answer: I understand that a gardener would want to intercrop beans which are legumes and fix nitrogen in the soil with their tomatoes which are heavy nitrogen feeders. The problem with castor beans is that they are not beans. They are just called that because their seeds look like beans. Castor beans are actually small tropical trees that grow to 15 feet tall. They would compete with your tomato plants for nitrogen and other nutrients as well as for water. And because of their height and broad leaves, they would shade your tomato plants which would suffer from a lack of sunlight, water, and nutrients and probably not fruit well if at all. I think it would be best if you planted your castor beans somewhere else in your garden/yard where they would not interfere with your other plants.
© 2019 Caren White
Caren White (author) on August 22, 2020:
I live in a temperate climate so I don't know much about greenhouses in warmer climates. I would guess that it would be difficult to prevent a greenhouse from overheating in a sub-tropical climate. That is a problem here during the heat of summer; keeping the plants cool enough so that they don't die.
Tshewang yeshi on August 21, 2020:
Is it feasible to have nursery raising in greenhouse in sub tropical region?
Jomasco on April 18, 2019:
My appreciation to Caren White for taking the time to answer my question. It is so gratifying knowing that there is always a good soul that enjoys the pleasure on sharing the acquired knowledge with others.
Caren White (author) on April 17, 2019:
The bean seeds do not have a top or bottom. You can drop them into a planting hole in any position. The seedling that emerges senses gravity and naturally grows against it which will result in the seedling growing upwards out of the soil. The roots will grow in the opposite direction, downwards into the soil.
Jomasco on April 17, 2019:
I like to know the position of the bean seed when planting it.