Crown of Thorns
A thorny, woody succulent that flowers almost year-round in a sunny window, in red, pink, yellow or white. Nearly indestructible, but the milky sap is a skin irritant and it is toxic to pets.
Crown of thorns is the plant for a hot, sunny window that nothing else survives. It flowers nearly continuously in good light, it tolerates drought, and it shrugs off heat. The trade-off is thorns and a sap that irritates skin, so it is not one for a household with small children or nibbling pets.
The newer Thai hybrids have bigger flowers and fewer thorns and are worth seeking out.
Light
Full sun, or as much as you can manage. A south or west window. It flowers in proportion to the light it gets; in indirect light it survives but stops blooming.
Water
Water when the top inch is dry in the growing season, about every ten days in summer. In winter, every three weeks or when the stems start to look thin. It drops leaves when it dries out too far and regrows them when watered; that is normal, not a crisis.
Soil and potting
A gritty succulent mix. Repot every couple of years in spring, wearing gloves. It flowers well slightly root-bound.
Feeding
A half-strength balanced feed every six weeks in spring and summer.
Propagation
Stem cuttings in spring. Cut with gloves on, dip the end in cold water to stop the sap, let it dry for a few days, then root in dry mix.
In a hot, dry home
One of the best flowering plants for this climate. Full sun through a west window, dry air and heat are exactly right. Water a little more in high summer when it is in full bloom.
Crown of Thorns varieties
Same care, different look. These are the named forms you will see for sale.
- Pink
Pink bracts.
- Yellow
Yellow bracts.
- Dragon Bone (lactea)
Euphorbia lactea: ridged, candelabra stems with white marbling. Same care.
- Red Trigona
Euphorbia trigona Rubra: three-sided upright stems flushed red.
- Devil's Backbone
Euphorbia tithymaloides: zigzag stems with variegated leaves.
- Mermaid Tail (lactea cristata)
A crested, fan-shaped Euphorbia lactea.
- Ghost (lactea White Ghost)
A pale, near-white Euphorbia lactea.
- Pencil Cactus
Euphorbia tirucalli: pencil-thin green stems; Sticks on Fire is the red form. Very caustic sap.
Problems and fixes
Leaves dropping
Likely cause: Drought stress, or a sudden change in light
Fix: Water, and keep it in one place. Leaves regrow along the stems.
No flowers
Likely cause: Not enough sun
Fix: Move into direct light.
Soft, blackening stems
Likely cause: Overwatering, especially in winter
Fix: Stop watering, cut away rot, and re-root healthy stems.
Crown of Thorns questions
Is crown of thorns toxic to pets?
Yes. The milky sap irritates the mouth and stomach of cats and dogs and can irritate human skin and eyes. Handle with gloves.
Why is my crown of thorns dropping leaves?
Usually because it dried out too far, or its light changed. It regrows leaves once conditions settle.
How much sun does crown of thorns need?
As much as possible. It flowers in proportion to sunlight and is happy in a hot south or west window.
Plants with a similar rhythm
Kalanchoe
- Light
- Bright indirect to direct sun
- Water
- Every 10 days
- Pets
- Toxic
Jade Plant
- Light
- Bright indirect to direct sun
- Water
- Every 2 weeks
- Pets
- Toxic
