Plant of the Week
Castor Bean, Mole Bean
Latin: Ricinus communis
 The bold look is back in garden design, so not
surprisingly, castor beans have reappeared as backdrops for gardeners
wanting to make a prominent statement in their plantings. Everything
about castor bean is bold and a bit audacious, so gardeners with a bit
of maverick in them seem to be drawn to this big plant.
Castor bean (Ricinus communis) is a member of the spurge
family and is native to tropical Africa where it grows as a tree to 40 feet
tall. When grown as an annual it is usually a more modest 10 feet tall. Its
leaves are star shaped with five to nine lobes and can be as large as a garbage
can lid. The selections grown as ornamentals usually have a maroon tinge to the
foliage.
The flowers of castor bean are borne near the top of the plant
in panicles. But lacking petals they are not especially noteworthy. As the seed
mature, the three-celled, spiny capsules turn bright red on foot long panicles
and make an interesting distraction to the bold foliage.
The castor bean seed looks like an engorged dog tick in size and
shape. It is from the extracts of this seed that castor bean gains its real
significance. The oil is used commercially for everything from lubrication to
cosmetics and is one of the most important industrial crop oils.
Like most children of my generation, my first encounter with
castor oil was as a not-so-gentle laxative. The purgative powers of castor bean
have long been known. The ancient Egyptians believed that food was the source of
disease, so they drank beer laced with castor bean three times a month for a
hearty flush of the digestive track.
As a teen-ager my encounter with castor bean expanded when I
tried Castrol motor oil in hopes it would make my old Ford run like a race car.
It didn’t help. The oil is used commercially in cosmetics, medicine and
waterproofing treatments.
But castor bean seeds have one other characteristic that merits
attention - they are poisonous. The poison is ricin, a proteinaceous molecule
similar in structure and mode of action to the bacterial toxin found in anthrax.
It’s said to be 1,000 times mote toxic than cobra venom.
Castor bean is sometimes called mole plant from the practice of
placing castor bean seeds in mole runs where the rodents will hopefully eat the
seeds and perish. When you spot a castor bean growing in the middle of someone’s
lawn, you can bet that the moles missed one.
Because of poor absorption of the phtotoxin from seed,
fatalities from accidentally ingested seeds are uncommon. In fact, I can find no
direct reports of fatalities from the seeds unless some nefarious plot was at
work. But prudence dictates that castor bean plants should not be planted if
small children are around.
Ricin has its own footnote in Cold War history. Georgi Markov
(1929 - 1978), a dissident Bulgarian journalist who worked for the BBC and Radio
Free Europe earned the animosity of Bulgarian State Security.
After his mysterious death in 1978, Scotland Yard investigated
and found embedded in his leg a BB that had been cross-drilled with holes. The
BB was fired from an umbrella rigged as a pellet rifle while Markov stood in
line at a bus stop. The holes in the BB had been packed with ricin.
Three schemes were uncovered in the US between 1991 and 1997 in
which ricin was intended to be used in murder. The most notorious of these
involved a separatist organization in Minnesota that plotted to assassinate a
local U.S. marshal by dosing the doorknob of his home with the poison.
Castor beans, despite their colorful history, are still good
garden plants. They are best used at the back of the flower border where they
form a fast growing, bold screen. Seeds should be planted where the plant is to
stand in mid spring after the last chance of frost is past. They do best in full
sun in any good garden soil. They are intolerant of wet locations.
By: Gerald Klingaman, retired
Extension Horticulturist
- Ornamentals
Extension News -
October 4, 2002
Back to Archives A - D
Back to Archives M - P
|
