A Pencil Cactus, Euphorbia tirucalli, is not a cactus plant at all but rather a member of the euphorbia family like a Poinsettia. This unique looking plant, native to Africa and India, is also referred to as Indian Tree Spurge, Naked Lady Plant, Aveloz, Milk Bush Plant, and Petroleum Plant. The green succulent stems of a Pencil Cactus, which are about the width of a pencil, branch upwards in an almost geometrical pattern. A Pencil Cactus grows quickly and can reach a height of 10′-15′ outdoors and up to 6′ in an indoor container. Although this is an easy care plant that just needs bright light and a little bit of water to do well, it does have a downside. All parts of these plants are considered poisonous and should be kept away from pets and children. Read more about common houseplants that are poisonous in Don’t Feed Me to Your Cat: A Guide to Poisonous Houseplants. This is a very different looking plant that I wouldn’t call beautiful and lush, but it is quite a conversation piece.
Plant Care
Light
A Pencil Cactus plant requires very bright light and can even handle direct morning sun.
Water
During the spring and summer allow the top 50% of the soil to dry out before watering. In the fall & winter water once a month. Pencil Cactus are very drought resistant, so when in doubt, do not water.
Fertilizer
Feed at the beginning of spring and the beginning of summer with a balanced 20-20-20 fertilizer at 1/4 the recommended strength.
Temperature
Likes warm temperatures between 65°-70°F (18.3°-21.1°C) during most of the year. In the winter, when resting, a Pencil Cactus prefers cooler temperatures around 50°F (10°C).
Humidity
Basic household humidity
Pests
Mealy bugs, spider mites, and aphids. Spray with my “Green Solution” (recipe in Glossary)
Diseases
Pencil cacti are susceptible to phomopsis which is a fungal disease that causes gray “wart like” growths on the stems and root rot due to over watering.
Soil
Use a quick draining succulent or cactus soil to prevent over- watering.
Pot Size
A pencil cactus grows quickly and becomes quite a tall plant. It needs a good size sturdy pot and may need to be re-potted every year or two. Allow the soil in the pot to totally dry out before moving a Pencil Cactus to a new container.
Pruning
Aggressively prune a Pencil cactus to keep it looking full. Always wear gloves and a long sleeved shirt when pruning the plant to prevent the irritating sap from getting on your skin.
Propagation
A Pencil cactus is easily propagated using stem cuttings.
Poisonous Plant Info
Pencil Cactus are very poisonous plants with a #4 toxicity level. The stems contain an irritating sap-like substance that oozes out of any cut or break in the stem. Not only should you wear gloves when working with a Pencil cactus , but you should wash your hands thoroughly with soap after removing the gloves. You don’t want to risk getting sap in your eyes or mouth.
FAQ
After taking a stem cutting from a Pencil Cactus Plant for propagation, dip the cut end of the stem in fresh water to stop the flow of the latex, sap. Allow the cut end of the stem to dry out for a week until it forms a callous on the tip. When the Pencil Cactus cutting is ready, pot the cutting in moist sand or in some cactus soil.
Repotting a Pencil Cactus Plant is a little tricky because of the danger of root rot due to over-watering. You should only re-pot a Pencil Cactus Plant when it is really necessary and then only during the warm months. Be sure the soil is very dry before you start, then gently remove the Pencil Cactus from its pot. Brush off the soil from the roots and remove any dead roots. If you accidentally make any cuts in the stems of the Pencil Cactus, immediately treat them with a Fungicide. Put the Pencil Cactus in its new container and spread out the roots. Fill in around the roots of the Pencil Cactus with moist succulent or cactus soil. Allow the soil in the pot to dry-out for a week or so, then begin to water lightly to reduce the risk of root rot. Since the Pencil Cactus is in a larger pot, it will take longer to try out.
The leaves on the stems of a Pencil cactus Plant naturally fall off very quickly. You are not doing anything wrong. A Pencil Cactus usually just has its long thin cylindrical succulent stems.