The pencil cactus (Euphorbia tirucalli) is an interesting shrub with succulent foliage that’s native to semi-arid tropical climates. It can grow quite large in the wild. Mature plants feature thick brown branches with clusters of smaller green branches at their ends, which are cylindrical in shape and around the thickness of a pencil (hence the plant’s common name). On the branches are oval leaves that grow up to an inch long. Also, in the late spring and early summer, small flowers appear at the ends of the green branches. This plant lacks the sharp spines that are commonly found on many cacti.
The pencil cactus is often grown as a houseplant, though care must be taken due to its toxic components. While you generally can start a houseplant year-round, it’s best planted at the beginning of the growing season in the spring. And unlike many cacti, this plant does have a fairly fast growth rate.
|Botanical Name||Euphorbia tirucalli|
|Common Names||Pencil cactus, Indian tree spurge, pencil tree, milk bush|
|Mature Size||20–30 ft. tall, 6–10 ft. wide (outdoors), up to 6 ft. tall, 1–3 ft. wide (indoors)|
|Sun Exposure||Full sun|
|Soil Type||Sandy, well-drained|
|Soil pH||Acidic, neutral|
|Bloom Time||Spring, summer|
|Hardiness Zones||11–12 (USDA)|
|Native Area||Africa, Asia|
|Toxicity||Toxic to pets and people|
Watch Now: How to Grow a Pencil Cactus (Euphorbia tirucalli) at Home
Pencil Cactus Care
The pencil cactus is incredibly low maintenance and can handle a lot of neglect. It also doesn’t usually have issues with pests or diseases. If you tend to travel a lot and don’t have time to regularly take care of a houseplant, this might be the plant for you.
Generally, watering this plant is only nevessary a couple times a month during the warmer parts of the year and even less during the cooler months. And fertilization is typically done annually. Other maintenance might involve pruning off dead stems as needed and repotting container plants as they outgrow their pots.
The pencil cactus prefers to grow in full sun, meaning at least six hours of sunlight on most days. However, it can tolerate a bit of shade and might even appreciate some protection from hot afternoon sun. Indoors, grow it by your brightest window.
This plant loves dry, sandy soil that isn’t highly rich in nutrients. Container plants do well with a succulent or cactus potting mix that doesn’t retain moisture.
The watering care for this succulent is very easy. It only needs water every two to three weeks in the spring and summer. Reduce watering to monthly in the fall and winter. It's preferable to let the soil dry out completely in between waterings to avoid overwatering. This plant is highly tolerant to drought, and too much water can rot its roots.
Temperature and Humidity
The pencil cactus thrives in warm temperatures ranging from 65 to 75 degrees Fahrenheit. Temperatures around the plant should not drop below 50 degrees Fahrenheit. Indoors, be sure to protect your plant from cool drafts, including those from an air conditioner. The plant also thrives in low humidity. But a higher humidity level shouldn’t bother it as long as the soil doesn’t retain moisture.
This plant isn’t a heavy feeder. Feed your pencil cactus with a balanced liquid houseplant fertilizer in the spring, and it should be fine for the rest of the year.
Propagating the Pencil Cactus
A pencil cactus can be readily propagated from cuttings. Always wear protective clothing during this process. Take a cutting of a green branch around 6 inches long, and dip it in fresh water to stop the flow of sap. Then, allow the cutting to dry for about a week and form a callous over the cut end before potting it in moist succulent or cactus potting mix.
Potting and Repotting the Pencil Cactus
When growing the pencil cactus in a container, it’s best to choose an unglazed clay pot that allows excess moisture to evaporate through its walls. Also, make sure there are ample drainage holes in the pot.
The plant can handle being a bit cramped in its pot. But once the roots have filled the container, plan to move your plant to one pot size up. Make sure the soil is dry before you begin repotting. Gently remove the plant from the pot, and knock off excess soil. Trim off any roots that look shriveled and dead or black and rotten. Then, put the pencil cactus in its new pot, and fill around it with fresh potting mix. Wait about a week before watering the plant.