Pencil cactus is a fitting common name for Euphorbia tirucalli, even though the plant would be useless for writing and is not really a cactus.
A single plant looks like many slender, green pencils, each stuck on the end or growing off the side of the one before it.
Lack of thorns is one indication that this plant is no cactus. Even more telling is the milky sap that oozes from broken or cut stems. That sap and the plant’s flowers – not very showy and rarely appearing indoors – put pencil cactus in the spurge family, along with more familiar houseplants such as poinsettia and crown-of-thorns.
On the negative side, the sap has been implicated as a potential carcinogen and, if it gets in the eyes, is said to cause temporary blindness.
MAKING NEW PLANTS
All that is necessary to get a pencil cactus started is to snap a few stems, each 2 or 3 inches long, from an existing plant (again, avoiding touching the sap). My pencil cactus cuttings came from a living fence I happened upon during a recent visit to Florida.
There was no need to keep those cuttings moist until I returned home because this plant, like all succulents, roots best if its cut ends are allowed to callous over in dry air before being put in soil.
GROWING THIS PENCIL
Where winter temperatures don’t drop below freezing, pencil cactus can grow outdoors as high as 30 feet. There, the dense tangle of stems and a sap that virtually every animal avoids make the plant an ideal living fence.
Where winters are too cold to grow pencil cactus outdoors, it makes a nice houseplant (keeping in mind the cautions about the sap). As a succulent, the plant loves light but otherwise tolerates the threats facing most houseplants: dry air and forgetful watering. If in doubt about whether or not to water this plant, don’t. It won’t die from under-watering. Taper off or completely avoid watering in winter. Extra perlite added to any potting mix further ensures that the mix drains well and stays dry.
One variety that’s particularly attractive indoors or out is “Sticks on Fire.” Its “pencils” are reddish yellow, the red becoming more prominent in cooler weather.
Once my pencil cactus plants take root and begin to grow, I may leave them to grow freely like a jumble of branching “pencils” in their pots. Or perhaps I’ll coax them with pruning and bending into a living sculpture. Perhaps I’ll pot them up with a candelabra cactus, another sculptural spurge (Euphorbia lactea, also erroneously called a cactus), which has fat, three-sided, dark green stems with thorns along the ridges.
No matter how I grow my new pencil cactus, I’ll be careful to avoid the sap.