How to Grow and Care for the Pencil Cactus

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—up to 30 feet tall and 6-10 feet wide. Indoors, the plant will stay at a more manageable 2-6 feet tall and 1-3 feet wide. 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.Although commonly known as pencil cactus, it's actually not a member of the cactus family.

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.The pencil cactus is often grown as a houseplant, though care must be taken due to its toxic components for both humans and pets.

Common Names	Pencil cactus, Indian tree spurge, pencil tree, milk bush
Botanical Name	Euphorbia tirucalli
Family	Euphorbiaceae
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
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 people, toxic to pets

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 necessary a couple of 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.

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 the hot afternoon sun. Indoors, grow it by your brightest window. It can also tolerate bright, indirect light.

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. Make sure to choose a container with good drainage.

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.

Pruning

Pruning a pencil cactus should be done in the early spring and is fairly easy. The sap from the pencil cactus is toxic, causing skin and eye irritation, and it will stain your clothing, so always wear protective clothing and gloves when handling this plant. Do not compost it due to its toxicity. Use a pair of pruning shears and first remove any dead or damaged branches from the cactus. Then clip off any branches to get the desired shape and height you want, making sure to cut down to the base of the branch. Take care not to take too much off the bottom part of the plant, as this plant does get top-heavy. Your pruning shears will be sticky afterward, so wipe them down with some rubbing alcohol when you're done.

Propagating the Pencil Cactus

A pencil cactus can be readily propagated from cuttings. Always wear protective clothing during this process. It is best to propagate your pencil cactus during the late spring or early summer when it is actively growing. Here's how:

1. Using pruning shears, take a cutting of a green branch around 6 inches long.
2. Dip it in fresh water to stop the flow of sap.
3. Then, allow the cutting to dry for about a week and form a callous over the cut end before potting it in a moist succulent or cactus potting mix.
4. Place it in a sunny area and lightly water. Let the soil dry out before watering again.

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.

Common Pests and Diseases

While the pencil cactus doesn't have many issues with pests and diseases, it is susceptible to a few. Spider mites tend to be the biggest issue, along with aphids and nematodes. These can be handled with neem oil. Overwatering and letting the soil stay wet can cause root rot, so always let the soil get completely dry before watering.

From: thespruce