The Most Poisonous Plant, Trees for Small Spaces

fruitful castor bean plants (Ricinus communis)

The most poisonous plant on earth, commonly known as castor bean, is growing along Roscoe Boulevard, between White Oak and Encino Avenues, in Northridge.  Did I say growing?  In fact, several robust specimens of it, nearly eight feet tall, are positively thriving there.

You can view this outcropping of castor bean (Ricinus communis) in a traffic island that comes between Roscoe Boulevard and a parallel, residential side street.  As you make your way along Roscoe, look to the south and you will notice some airy shrubs with bronze foliage and prickly, carmine red seed capsules.  There is no knowing how these plants ended up where they ended up, but I suspect a bird or a squirrel, as opposed to a human, was involved.
Castor bean is drought tolerant and extremely vigorous.  Sprouting from a seed, it can put on eight feet of growth in a single growing season without any irrigation other than winter rain.  Many ornamental cultivars of castor bean are available through the nursery trade.  In truth, it is possible that the Northridge castor bean plants were intentionally planted, as opposed to sprouting up as volunteers, since they do create an effective visual barrier to automobile traffic.
Fully processed ricin, which is extracted from castor beans or seeds and is used in biological warfare, is extremely toxic, with a few salt sized grains of it constituting a lethal dose.  By the same token, you would need to swallow 4-8 unprocessed seeds to suffer fatal consequences.  Still, some people have a skin reaction to mere contact with the seeds or leaves.  A member of the spurge family, it is a relative of poinsettia, a plant known for its allergenic sap.
As is nature’s way, anything that is highly toxic is also highly curative, when applied in the proper dose.  I remember swallowing teaspoons of castor oil, which is made from castor beans, as a child.  A half century ago, castor oil was administered as a preventive tonic for colds and flu.  Castor oil has long been reputed to have strong anti-microbial properties and thus helps fend off or mitigate bacterial, viral, and fungal infections.  Castor oil is also famous for its laxative effect.
In the Bible, the story of Jonah includes a fast-growing kikayon, which the Talmud identifies as a castor bean plant.  It grew up quickly and provided shade for Jonah after he succeeded in persuading the people of Nineveh to repent.  Even in Biblical times, the powerful curative properties of castor oil were well known and people would simply sit under castor bean plants as a means of treating a variety of illnesses.
We live at the eastern edge of the San Gabriel Valley and are looking to plant a new tree in our somewhat small yard.  We were thinking of a Japanese maple.  Our climate is very similar to that of the San Fernando Valley.  This tree would be in an east-facing yard.  This area gets sun all morning and really into the early afternoon, when it becomes more filtered sun.
Any suggestions on what variety would work well for us? We are looking for a tree that would stay on the smaller side and not have a root issue since it will be near the house and a small retaining wall.   
Linda Cline, La Verne
In more than 25 years of Valley plant watching, I have never seen a Japanese maple that did not show burnt leaves, including those exposed to a bare minimum of sun.  The biggest Japanese maples I have seen are growing in San Marino at the Huntington Gardens in the Japanese garden there.  The leaf edges of these trees turn crispy brown soon after they leaf out in the spring, but the trees themselves have clearly been growing there for several decades at least.  If crispy leaf edges are not a problem for you, then you could plant a green leaf variety.  The burgundy leaf Japanese maples do not grow well at all in our climate with even half day sun exposure.  Coral bark Japanese maple (Acer palmatum ‘Sangokaku’) is a distinctive cultivar owing to its salmon-orange-pink bark, making it a subject of colorful interest in winter after leaves have fallen.
Also, to ease acclimation, you should plant the biggest Japanese maple specimen you can afford.  I would invest in a 24″ box size, if at all possible, even though it will cost several hundred dollars or more.

mayten (Maytenus boaria)

There are other trees you might want to consider.  Magnolia ‘Little Gem’ is a slow growing magnolia that reaches around 20 feet at maturity.  You should also look at at the mayten tree (Maytenus boaria), a weeping tree that is also slow growing and of modest mature stature.

It might be something of a risk, but Michelia (my-KEE-lee-a), a magnolia relative, is a truly exceptional tree if you can provide proper conditions for growth.  Foliage is reminiscent of an avocado tree’s, only it is softer and lime green in color, and Michelia flowers have a wonderful fragrance.  Two species are available in the nursery trade:  Michelia champaca and Michelia figo.  Trees reach around twenty feet in height.  Again, I would plant the largest specimen I could find since Michelias are frost sensitive and larger trees have greater tolerance to cold and other stressors.
Finally, you might consider moderate sized Carolina laurel cherry cultivars (Prunus caroliniana ‘Compacta’ or Prunus caroliniana ‘Bright ‘n Tight’). These ornamental cherry trees have a glowing dark green leaf and a compact growth habit.

croton (Codiaeum variegatum)

Tip of the Week:  Croton (Codiaeum variegatum) is one of the toughest house plants.  Croton (KRO-tun) means tick in Greek and alludes to the shape of its seeds.   Croton’s waxy leaves emerge green but then turn to yellow, orange, red, or pink.  There are hundreds of croton cultivars, with each one displaying a particular foliar color emphasis.  As long as you do not over water, allowing soil to go bone dry between waterings, you should be able to keep a croton thriving for several years.  If leaves lose their color, it’s a sign of insufficient light exposure.  Croton is a relative of castor bean and poinsettia and its milky white sap, like theirs, may irritate the skin.

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