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written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

Some of you reading this column probably remember being given a teaspoon full of castor oil when you were a child. It served as a laxative and because of its horrible taste, sometimes it was also a punishment.

I wonder if mothers and grandmothers would have been so liberal with the stuff if they had known that Mussolini used it to coerce dissidents and opponents of his regime into submission. They were forced to consume large quantities of castor oil that could result in severe diarrhea, dehydration and potential death. Civilians and soldiers who said they were too ill to work, were administered less intimidating doses. This was done under the pretext that castor oil was good for you when you were sick. This pretext became a misconception that stayed around for years!

If you’re wondering why I’m talking about castor oil in a gardening column, please bear with me for just a bit. Believed to be native to northeastern Africa or the Middle East, the castor bean plant (Ricinus communis) has been cultivated for centuries for the oil produced from its seeds. Evidence exists that the Egyptians used it to fuel their lamps in ancient times. Today castor oil is still used (in moderation) as a laxative but it’s also a prized industrial lubricant. It’s also used to make various pharmaceuticals, paints, and biodiesel fuels.

The castor bean is not really a bean, although its seeds do look somewhat like those of the legume family. It’s really a member of the spurge (Euphorbia) family and is one of the most poisonous plants known to man. The oil administered to some of us as children for its laxative properties may have tasted like poison, but it wasn’t. However, the seed coat of the castor bean contains deadly toxins, known as ricin and ricinine. These poisons are also present in other parts of the plant, but in lower concentrations.

I’m bringing this up now because a local gardener brought me a picture of an exotic-looking plant from a neighbor’s yard. She likes the looks of the plant and wondered what it was. The plant does have a tropical, exotic appearance. In tropical climates the castor bean grows into a large shrub or small tree up to 40 feet tall and 15 feet wide. In temperate zones, it grows as an annual that can reach a height of 15 feet in one season. It’s truly an exotic looking plant with huge purplish to reddish-green palmate leaves with 5 to 11 deep lobes. The leaves can be one to two feet or more across with long purple to red stems (petioles).

The flowers of the native species of castor bean are not especially remarkable, but some of the cultivated varieties are quite showy with fat, bright red flower spikes, bright red leaf stems and more colorful leaves. The female flowers are replaced by brown, spiny globose seed capsules. Each capsule has three compartments with each compartment containing one of the “bean” seeds. When it dries, the capsule breaks open and shoots out the seed a distance from the plant.

It’s the seeds of the castor bean that are quite deadly. It can take up to eight beans to kill an adult, but much fewer, even just one, to kill a child. Ricin works by inhibiting protein synthesis and there is no known antidote. Some people may also experience a severe allergic reaction when they come into contact with broken seeds. For these reasons, I would recommend not growing castor bean in your garden, despite their exotic beauty. If you do have them in the garden, handle the plants and seeds only with disposable latex or plastic gloves. I would also recommend removing the flower spikes before they develop into mature seed capsules and start shooting out seeds.

Castor bean has been grown as an agricultural crop in the US on a limited scale, but it is currently grown more extensively in other parts of the world, especially India and China. In the US, it grows best in the southeast part of the country. Because it self-sows quite freely with its shooting seeds, it has escaped cultivation and become invasive in some states.

While you might admire this exotic-looking plant, it’s best left out of your garden, especially if there are young children around.

Published: 9/13/2008 1:40 PM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

An axiom that gardeners, horticulturists, and good landscape designers all try to adhere to is “planting the right plant in the right place.” You want to place a tree, shrub, or flowering plant where it will be able to grow the best and not cause you problems. However, there are some plants that shouldn’t be planted even if they’re well behaved and have the perfect place to thrive in the garden or landscape.

RED MAPLE: One such plant is red maple (Acer rubrum), one of my favorite shade trees for area landscapes. It tolerates our soil and climate conditions, it has amazing orange to red fall color, and it grows relatively fast. It also has few insect or disease problems. The red maple is one tough tree that I highly recommend, but it should never be planted anywhere near where horses are kept. That’s because the leaves are highly toxic to horses.

The Cornell Poisonous Plants Informational Database indicates that the toxic component of red maple leaves is gallic acid. When ingested by horses, gallic acid causes a problem called methemoglobinemia. In layman’s terms, the gallic acid causes a type of anemia brought on by damage to the red blood cells severely impairing their ability to carry oxygen to body tissues. The symptoms of poisoning are quite gruesome and a poisoned horse will often die within 18 hours to a week or more after ingesting red maple leaves.

It appears that the gallic acid content of the leaves and the potential for horse poisoning increases during the growing season. Wilted leaves are of greatest concern. Red maple owners only need to be worried if there are horses kept nearby. The leaves are not poisonous to humans or other animals. If there are horses at risk nearby, red maple owners should consider the removal of their tree. Once cut down it’s also important to make sure that no regrowth occurs from the stump. If limbs with leaves are removed from a red maple, they should never be placed anywhere that horses might browse.

There are a number of other species of admirable maples planted for shade in home landscapes … and possibly near horses. One might wonder if they also could pose a poisoning hazard. While gallic acid has been found in silver and sugar maple leaves, there have been no reports of horse poisoning. However, researchers indicate that hybrids of red maple crossed with silver maple may also have poisoning potential. They also point out that a number of people call the red to purple leaved Norway maple “red maple.” The true red maple and red maple hybrids have green leaves during the growing season and turn a bright scarlet to orange colors in the fall.

There are also some other trees known to be poisonous to horses. Horse owners are advised not to let a tree grow where the branches will overhang a pasture or paddock unless they know the tree is not poisonous.

DONKEY TAIL: The plant known as donkeytail, myrtle spurge, or creeping spurge (Euphorbia myrsinites) is native to Eurasia. It’s commonly planted by gardeners in low-water-use gardens and rocky garden areas. It’s hardy, drought tolerant and multiplies easily by seed. The yellow flowers and the blue-green leaves spiraling around the fleshy stems make it an interesting plant for the garden, but it really shouldn’t be planted anywhere.

There are two reasons to avoid this plant. First of all it’s considered a noxious weed and is listed as a Class B Noxious Weed in Washington. It has already escaped cultivation in Grant county and is proving difficult to control. While “pretty” , it’s aggressive and crowds out native plants that serve as forage for deer and other wildlife. The Washington State Noxious Weed board wants gardeners to stop growing this plant so that they can keep it from becoming a serious problem in Washington.

Another reason that gardeners should avoid this plant is its milky latex sap. The sap contains diterpene esters and causes serious skin irritation in the form of redness, swelling, and blisters. Anyone working with this plant should avoid getting any of the sap on their skin by covering up well and wearing rubber gloves and safety goggles. This is nasty stuff and is a big reason why it shouldn’t be planted in the garden.

Another well-liked euphorbia causes similar problems for gardeners, except it’s not a noxious weed. The sap of Snow-on-the-Mountain (Euphorbia marginata), a popular pretty perennial with white flowers, also causes skin blistering.

Published: 5/12/2007 2:51 PM



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