How to Grow the Pencil Cactus

pencil cactus by a window

The Spruce / Letícia Almeida 

In This Article

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
Plant Type Shrub
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
Flower Color Yellow
Hardiness Zones 11–12 (USDA)
Native Area Africa, Asia
Toxicity Toxic to pets and people
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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. 

closeup of a pencil cactus
The Spruce / Letícia Almeida  
macro shot of pencil cactus
The Spruce / Letícia Almeida 

Light

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.

Soil

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. 

Water

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. 

Fertilizer

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.

Is the Pencil Cactus Toxic?

It is always recommended to wear protective clothing, especially thick gloves and eye protection, when working with a pencil cactus. Plus, the plant should be kept out of the reach of children and pets. This is because the sap inside the pencil cactus, which can be released when a stem is broken, is toxic to both people and pets. Toxicity can occur both from ingesting the sap and via skin contact. 

Symptoms of Poisoning

When the sap gets on the skin of a person or an animal, it can cause redness, burning, rashes, blistering, and other irritation. It can be especially dangerous to get the sap in your eyes. Besides being very painful and causing redness and swelling, blindness can occur from the toxin. When ingested, the pencil cactus can cause serious irritation to the GI tract, vomiting, and diarrhea. Ingesting a high quantity can be fatal, but the unpleasant taste of the plant usually prevents this from happening. Furthermore, the toxin also can cause an anaphylactic reaction in people and animals who are allergic. If you suspect poisoning, contact a medical professional immediately for emergency care.

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.

taking cuttings from the pencil cactus
The Spruce / Letícia Almeida  
pencil cactus cutting in water
The Spruce / Letícia Almeida 
placing the calloused cutting in new soil
The Spruce / Letícia Almeida 

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.

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