Light
Full sun or the brightest window you have. Outdoors in a hot summer, a little afternoon shade helps. Sun is also what colors firestick, whose branch tips turn orange and red in strong light.
Water
Water about every week or two in spring and summer, and let the soil dry out in between. Water much less in winter. It's drought tolerant, and too much water rots the roots.
Soil & pots
A fast-draining mix with plenty of grit, such as coarse sand or perlite, in a pot with a drainage hole. A heavy pot helps, since tall plants get top-heavy.
Temperature
Frost tender. It lives outdoors year-round only in zones 11 and 12, and just about survives in the warmest parts of zone 10. Indoors, normal room temperatures are fine, and it does best with nights above 50°F (10°C).
Is pencil cactus safe for pets?
Toxic to cats and dogs. ASPCA lists pencil cactus as toxic to cats, dogs and horses. The sap irritates the mouth and stomach and can cause vomiting and drooling. In the eyes it can cause corneal ulcers in severe cases.
Propagation
Pencil cactus roots readily from stem cuttings in spring or summer. Gear up first, because every cut bleeds milky sap.
- Wearing gloves and eye protection, cut a piece at least 6 inches long.
- Let it air dry for 4 days to a week until the end calluses.
- Stand it in dry, gritty mix and water lightly.
- Expect good roots in about a month.
Common problems
FAQ
Is pencil cactus a cactus?
No. It's a Euphorbia, in the spurge family, related to poinsettia and crown of thorns rather than to cacti. It has no spines, and the "pencils" are green branches carrying a few tiny leaves that drop early.
Is pencil cactus sap dangerous?
Yes. The milky sap can cause mild to severe skin irritation, and in the eyes it can damage the cornea, sometimes permanently. Wear gloves and eye protection when you handle it. If sap gets in your eyes, get medical help right away.
Is pencil cactus toxic to cats and dogs?
Yes. The ASPCA lists it as toxic to cats and dogs. Chewing it irritates the mouth and stomach, and sap in the eyes can hurt them. Keep it where pets can't brush against it or chew it.
What's the difference between pencil cactus and firestick plant?
They're the same species. Firestick is the red-tipped form, sold as 'Sticks on Fire', 'Sticks of Fire' or 'Flame'. Its color is strongest in winter and strong sun, and it can fade toward yellow in summer.
How big does a pencil cactus get?
Indoors, usually 2 to 6 feet tall. Outdoors in frost-free places it becomes a tree of 20 to 30 feet, so it's best kept in a pot unless you have room.
Sources
- Euphorbia tirucalli (Plants of the World Online, Kew)
- Pencil Cactus (ASPCA Toxic and Non-Toxic Plants)
- Are Succulents Safe to Have Around Pets? (ASPCA)
- Euphorbia tirucalli (NC State Extension Plant Toolbox)
- Euphorbia tirucalli (UC ANR, Plant Safely in Drought-Tolerant Landscapes)
- Euphorbia tirucalli (Missouri Botanical Garden Plant Finder)
- Plant Profile: Pencil Plant (UF/IFAS Extension Putnam County)