Euphorbia keithii
Swazi euphorbia
Uncommon densely branched, shrubby succulent becomes treelike with time, developing a stout trunk. Excellent selection for pots, hot spots.
 |
height |
6–18ft |
 |
width |
6–12ft |
 |
tolerates |
Drought, Deer , Gophers, Heat, Pots, Rooftops, Wind |
 |
water
needs |
Low |
 |
water
info |
Columnar euphorbias are very drought tolerant but will grow faster if they receive some summer water, usually every couple weeks to a month once established (let the plant dry out between waterings). If you aren’t getting summer growth you may be underwatering. This plant is from subtropical Swaziland (and possibly SW Mozambique) and as such prefers a dry winter; outdoors in central California, they will not need supplemental winter water once established, given rain every month or so. |
 |
hardy
to |
35F |
 |
exposure |
Part Shade – Full Sun |
 |
indoor
outdoor |
In or Out |
 |
drainage |
In Ground: Cactus Mix, In Pots: Cactus Mix, Tolerates Sandy Soil |
 |
fertilizing |
All Purpose, Low Needs |
 |
origin |
E Swaziland |
 |
california
native |
No |
 |
sunset
zones |
17, 22–24, H2 |
SUNSET ZONES MAP
Growing Notes
Columnar euphorbias can get surprisingly large, so be sure to note the size, and place your plant accordingly.
They respond well to pruning. They will look scarred for a while, but then will push new growth wherever they are pruned, often giving you several new growth points. Take care when pruning, as euphorbias have toxic sap that can cause a skin rash or damage to the eyes (make sure to rinse repeatedly with water if sap gets on your skin or in your eyes).
They like a warm sunny exposure but do surprisingly well in shady areas as long as they are not given extra water during winter.
As columnar euphorbias grow they will transition from colorful and smooth new growth to dull, brown and rough older growth. This is called corking, and it is totally natural. Think of this like an oak tree where the new shoots are shiny and green, but then eventually you get a trunk covered in rough dull bark.
Soft dark brown spots on Euphorbia are usually a sign of rot. Carve these spots out with a sterile knife immediately (carve all the way back to healthy-looking tissue). Rot usually results from overwatering, but it can also be caused by drastic under-watering. Occasionally this will start at the base of the plant, which means the roots have rotted. If you would like to save the plant you will need to remove the top above the rotten base, let the top sit for two weeks in a shady spot, and then replant in very sharp-draining soil. Place the cutting in a warm spot to re-root, preferably not in harsh sun.
Special Interest
In the movie “The Gods Must be Crazy,“ a villain hides under a columnar euphorbia, only to be outwitted when his pursuer shoots the plant, pouring down toxic sap all over him. Clearly the screenwriter knew their plants!
These plants are often confused with columnar cactus because, through convergent evolution, they have adapted into a similar form. However, euphorbias are not closely related to cactus. In fact they’re more closely related to the holiday poinsettia. Some notable differences are euphorbia’s latex sap, insignificant flowers, tiny little leaves when in growth, and thorns instead of spines to protect themselves.
More Info
This plant also makes a good houseplant. If you allow this plant to go bone dry indoors and then try to water it, the water will run down the sides of the pot and out the bottom. You will think you watered the plant, but you have not! The soil is still dry! When your euphorbias soil goes bone dry, it becomes hydrophobic, which means the soil is so dry that it resists absorbing moisture, like a dry sponge. Be sure your plant reaches saturation by over-watering until there is standing water in the saucer. Add more water each time it is soaked up. Eventually the water will stop being absorbed and remain in the dish. Your plant is now saturated and the water should be removed.
Sometimes when placed too close to a direct sun window, you will get burning along the flat side of the plant. It is better to arrange the plant at a glancing angle from the light, or keep it a couple feet back from the window. This burning will not hurt the plant long term, so it is only an aesthetic issue.
