Crown of Thorns
Euphorbia milii · the Christ Plant
It grows on hot, dry, rocky ground in Madagascar, a thorny succulent shrub that flowers almost all year. The showy red, pink or yellow 'petals' are not petals at all. They are a pair of coloured leaves called bracts, and the true flowers are tiny and green between them.
Family
Euphorbiaceae
Origin
Madagascar
In the wild
Dry rocky ground
Indoors
Around 0.6 m
Growth
Slow to moderate
With pets
Toxic
Where it's from
Madagascar
Madagascar dryland
Endemic to hot, sun-exposed, rocky and sandy sites, where it sprawls to five or six feet.
Outdoors: zones 10–12
Damaged below about 1.6°C and not frost-hardy. A patio plant at most where it gets cold.
Armed with thorns
True thorns up to three centimetres long, black, dense along the water-storing stems. Grown as a barrier hedge.
It has a public-health job
The World Health Organization has recommended Euphorbia milii for snail control, targeting the snails that spread schistosomiasis. The same milky latex sap that makes it useful is what makes it toxic: an irritant to skin, eyes and gut.
Blooms nearly all year
One of the rare houseplants that reliably flowers indoors, often from late winter well into fall.
A quirk in its paperwork
Succulent euphorbias are CITES-regulated, except this one when shipped in nursery batches of 100 or more.
Let the cut bleed first
Take a cutting and it bleeds milky sap. Let the wound dry and callus before potting, wearing gloves.
How to keep it
LightFull sun
Six or more hours. It needs strong light to bloom. Some midday shade helps in very hot climates.
WaterSoak then dry out
Intolerant of wet soil, especially in winter. Cold wet soil is the number one killer.
HumidityLowTolerates dry indoor air. No misting.
TemperatureWarm, above 10°CDoes not tolerate below about 10°C. Not frost-hardy.
SoilSandy, gritty, fast-drainingA cactus mix or gritty soil. It even tolerates poor, rocky ground.
FeedingLight, in growthA light feed in the growing season only.
DifficultyEasyBeginner-friendly and drought-tough. Overwatering and cold are the only real risks.
With petsToxicThe milky latex sap. Mouth and gut irritation, vomiting, drooling, and skin and eye irritation from contact. The bitter sap means animals usually self-limit.
PropagationStem-tip cuttingsLet the cut sap dry and callus, then root in gritty mix. Wear gloves.
RepottingEvery 2–3 yearsInfrequent. It sulks if overpotted in wet soil.
What the data says
What it costs
Common and cheap as the base plant. The colourful Thai hybrids are a small collector niche.
$10–25
Showy bicolour Thai and 'Giant' hybrids with large bracts run higher, around $20 to $50 and up.
IUCN · Data deficient
In the wild
A Madagascar endemic thriving by the million indoors while its wild self is a thin, threatened sliver.
The cultivated plant is in no danger. But the only formal assessment found, for the old variety splendens in 2004, is Data Deficient, noting its wild range in degraded parts of Madagascar may be very reduced. Abundant on windowsills, imperilled at home.
When it sulks
Mushy stems, rot at the baseOverwatering or cold wet soil. The main killer.
Bare, spiny stemsNormal seasonal leaf shedding, or stress from cold, dark or drought.
Few or no flowersNot enough light. It needs full sun to bloom.
Leaf spots or blightToo damp, or poor airflow.
PestsScale, mealybug, thrips and spider mites.
Varieties & company
The varieties
var. splendensRed HotCrimson SplashPeppermint CandyThai Giant hybrids
Pairs with · keep apart from
CactiAloeSnake PlantMonsteraFernsPeace Lily
A new plant, every week.
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