Gardening: Castor bean plants contain two types of poison

For the News-DemocratJuly 5, 2013 

Q. Is it safe to plant castor beans on the edges of a vegetable garden? I know they are poisonous. They are attractive plants.

-- J.L. of Troy

A. Castor beans (Ricinus communis) are very poisonous. Most botanical references list this plant as the No. 1 poisonous plant in that it actually contains two poisons -- Ricin and RCA-agglutinin.

Ricin is found in the seed coat and a little in the leaves of the plant. RCA agglutinin is found in various tissues of the plant but not the flower or seed.

RCA agglutinin can cause dangerous blood clots. Both of these poisons have to be ingested to cause any problems. So make sure that no one eats the seeds.

In spite of all this, many of us were given castor oil for digestive problems when we were small. This castor oil was made by compressing the seeds of the castor bean plant.

The seed pods do produce some hard thorny looking tissue which keeps many animals and humans from picking them. But when they get older, the pods split open and show some marbled brown and tan seeds that look like other bean seeds. Some other varieties produce reddish to reddish-brown seeds.

Castor bean plants are very attractive, with leaves that have five to 12 lobes. They can have dark green to a pinkish red and even a white or yellow variegated leaf, depending upon the variety. With the rain we are having this year, they could grow up to 6 to 7 feet tall. However, in last year's head and drought, some grew to only 3 feet tall.

Castor bean plants have the reputation for producing an odor that keeps moles away. Some gardeners plant castor beans completely around the vegetable or flower garden for this reason. Other people plant them around the perimeter of their yard to keep the moles out of lawn areas. There are new products being sold that mix castor oil with water to spray on the lawn to keep moles away. If you try to do this yourself, the water and oil will just glob together and stop up a sprayer.

Planting castor beans around a vegetable garden will work if you allow enough space for your row of castor beans to be about 1 foot away from your growing vegetables. Castor bean plants spread about 3 feet in radius, so keep this in mind.

In many parts of the United States, castor bean plants are ground into pumice, which is used as a fertilizer similar to cotton seed meal. Other growers save the hulls of castor bean seeds to spread in their orchards.

Q. My pole beans have some rust- colored areas on the pods. What is this and what can I do about it?

-- H. L. of Collinsville

A. You actually named your problem without knowing it. Rust is a fungus that attacks beans when the weather conditions are exactly what we are experiencing -- cooler than normal and very moist. The rust spores are found in the soil from bean plants that had this disease as long as five years ago. These spores get blown on to the plant or splashed upward with raindrops. The spores grow on the bean pods, and when the spores mature they may be blown or splashed onto nearby developing bean pods.

A vegetable fungicide will prevent the disease from spreading but will not cure the beans pods that have them already.

Charles Giedeman is a local contributing writer. Send your gardening questions to Lifestyle Editor Pat Kuhl, Belleville News-Democrat, P.O. Box 427, 120 S. Illinois St., Belleville, IL 62222-0427. Or email to

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