How to Grow Castor Beans

Updated on February 14, 2019
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Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.

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Castor beans have gotten a bad rap as a source of the poison ricin. The truth is that the beans have been used for thousands of years and the plants add a tropical touch to your garden.

What are Castor Beans?

Castor beans 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 sometines start out red and turn to green as they mature. Newer cultivars were bred so that the leaves stay red.

Castor bean plants produce both male and female flowers on the same plant.
Castor bean plants produce both male and female flowers on the same plant. | Source

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.

When the seeds are ripe, the fruits open and forcefully eject the seeds.
When the seeds are ripe, the fruits open and forcefully eject the seeds. | Source

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 and 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 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.

Castor bean seeds look like beans.
Castor bean seeds look like beans. | Source

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, 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 up on 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.

Castor bean seedling that has been direct sown in a garden.
Castor bean seedling that has been direct sown in a garden. | Source

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.

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 seedling 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.

Castor bean seedling that has been started indoors
Castor bean seedling that has been started indoors | Source

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

  • My neighbor gave me a castor bean plant to transplant. It was 3 feet tall. It’s drooping badly. Should it be cut down?

    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.

  • Can I plant castor beans in the same pot as tomatoes plants?

    No, both are enormous plants and wouldn't fit in the same container. They should be grown in separate pots.

  • How far apart should the rows be? I know in tow you said 4 feet apart but what is the distance between rows?

    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.

© 2019 Caren White

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    • profile image

      Jomasco 

      7 months ago

      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.

      Thanks Caren

    • OldRoses profile imageAUTHOR

      Caren White 

      7 months ago

      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.

    • profile image

      Jomasco 

      7 months ago

      I like to know the position of the bean seed when planting it.

      Thankyou.

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