Pencil Cactus Care and Propagation Explained

The pencil cactus (Euphorbia tirucalli) also known as fire stick or milk bush is a small succulent tree native to semi-arid tropical climates of Africa and India. This plant releases toxic sap when bruised, which can cause skin irritation, eye pain, and a burning sensation in the mouth.

Euphorbia tirucalli has smooth cylindrical stems with fragile succulent twigs about the thickness of a pencil. It can grow quite large in the wild but indoors the plant can stay to a manageable size of about 2-6 ft. tall and 1-3 ft wide. Mature plants feature small oval leaves that fall off easily.

In summary, here is what to know about the pencil cactus.

Common names	Pencil cactus, fire stick, milk bush.
Botanical name	Euphorbia tirucalli
Mature size	20–30 ft. tall, 6–10 ft. wide (Outdoors)
Light exposure	Full sun to bright indirect light.
Soil requirements	Sangy, well-drained potting mix.
Blooming	Late spring to early summer, yellow flowers.
Hardiness Zones	USDA zones 11 – 12.
Toxicity	Poisonous to humas and pets.

Pencil cactus care

The pencil cactus is one of the easiest plants to care for. Watering is minimal probably a couple of times during the drier months and even less during winter. Fertilization either doesn’t have to be on a monthly basis during the growth period, it can just be done annually.

This plant usually doesn’t have pest or disease problems. You might just need to inspect it and prune off dead stems to keep it looking great. Repoting can be necessary as the plant outgrows its pot. Being a poisonous cactus plant, you must keep it out of reach of children and pets.

Light requirements

Pencil cactus prefers full sun, meaning at least six to eight hours of direct sun. It can also survive in bright indirect light or a bit of shade. Indoors, grow it near a south-facing window or a spot that receives maximum sunlight. You may use artificial grow lights in areas without enough sunlight.

Your pencil cactus may start to etiolate if you don’t provide it with enough light. This means that the plant will stretch towards any light source, resulting in a spindly or long, thin appearance. The cactus etiolation can be fixed by moving the affected plant to a brighter location.

Well-drained soil

The pencil cactus thrives in sandy, well-drained soil. When growing it in a container, it’s best to use a cactus potting mix. You can also make your own cactus potting mix but make sure it has more sand for improved drainage. Poor draining soil is known to cause root rot in all succulents.

Additionally, you’ll need to use a pot with ample drainage holes. I recommend you use unglazed terracotta clay pots, they have porous walls that allow excess moisture to evaporate from the soil. 

Infrequent watering

As said, pencil cactus needs infrequent watering and less during winter. Water it every two to three weeks but allow the soil to dry completely between the waterings. As a rule of thumb, water cacti and succulents only when the soil is completely dry. Overwatering can cause root rot and other fungal issues.

Root rot is a critical plant condition caused when the roots suffocate and die due to insufficient oxygen resulting from the excess water in the soil. Fungi and bacteria that cause root rot also thrive in damp soil conditions. Treating root rot is difficult but you can save the plant by reporting it in fresh soil.

Temperature and humidity

The pencil cactus is native to semi-arid tropical regions and it’s adapted to warm temperatures. The temperature around the plant should range between 65°F and 75°F and not below 50°F. Average home humidity should be fine for this plant but protect it from cold drafts and heat sources.

Fertilization

You typically don’t need to fertilize a pencil cactus very often. However, you can fertilize it once during spring or summer to boost growth. Use a well-balanced houseplant fertilizer and apply as directed on the label. Other organic supplements like worm compost tea can also benefit the plant.

Pruning

Pruning pencil cactus should be minimal, only when you need to cut off dead stems or keep them in a desired shape. This is best done in spring or summer when the plant is actively growing. You should be extra careful when pruning the pencil cactus to avoid contact with its toxic sap.

The milky sap will also stick on your pruning shears and you should remember to clean it off before storage. Use rubbing alcohol to remove the sticky substance.

Repotting

The pencil cactus is likely to outgrow the pot over time. To prevent the problem of rootbound, repot the plant after every two to three years. Be sure to transplant into a pot that is a size bigger than the current one. It should also have great drainage including the soil.

How to propagate pencil cactus

Pencil cacti can be easily propagated from stem cuttings. To start, you’ll need a healthy pencil cactus stem, a clean sharp knife or shears, a pot with drainage holes, a cactus potting mix, and a rooting hormone (optional).

Propagation directions:

1. Using your sharp knife, take a cutting from a healthy pencil cactus stem, about 4 to 6 inches long.
2. Allow the cutting to dry out for about 5 days so that the cut end can callous over. This will prevent the cutting from rotting.
3. Plant the cutting in a pot filled with your cactus potting mix and make sure about 1 or 2 inches of the cutting is inserted in the soil. You may apply your rooting hormone at the cut end before inserting the cutting in the soil.
4. Mist the cutting with water to make the soil moist but not waterlogged, then place the pot in a sunny area.
5. Keep monitoring the cutting and water it only when the soil is completely dry. You may test the moisture by inserting your finger in the soil.
6. Once the cutting has rooted, you’ll see some purple growth forming on the stem and you can transplant it or provide care as you would for established plants.

While stem cutting is the easiest way to propagate pencil cactus, the process needs some patience. It may take several weeks or even months for the cuttings to root. Rooting and growth rates commonly depend on the climatic conditions of a region.

Common problems and fixes

The pencil cactus is quite resistant to most plant diseases but it is prone to root rot when overwatered or grown in poorly draining soil. To avoid this problem, let the soil dry out completely before watering, ensure the pot drainage holes are working and use succulents soil mix when potting or repotting.

Plants that are completely neglected can also be infested with insect pests including spider mites, aphids, scales, and mealybugs. Most houseplant pests can be controlled with neem or insecticidal soap. Be sure to use the product as directed on the label.