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full sun (6 or more hours of sun hitting the leaves per day. South-facing window, no obstructions. Under grow lights, keep them 4-8 inches away for 12-14 hours) - at least 6 hours of direct light daily. This is non-negotiable; low light (more than 8 feet from a window, or a north-facing room. A grow light 10-12 inches away works great if your windows are not cutting it) means no blooms and sad, leggy stems.Light
Allow soil to dry out almost completely between waterings. water thoroughly (water until it drains out the bottom. Empty the saucer after 30 minutes so the roots are not sitting in water), then wait. Overwatering is the number one way to kill this plant.Water
Prefers low humidity. Average household air is fine; it actually dislikes the misting (note: misting does not actually raise humidity meaningfully. A pebble tray or humidifier is more effective) treatment you'd give tropical plants.Humidity
65-90°F (18-32°C). Hardy in USDA Zones 9a-11b outdoors; bring inside well before any frost.Temperature
easyDifficulty
Euphorbia milii plant

Crown-of-Thorns

Euphorbia milii

Easy

Crown-of-Thorns is a spiny, multi-stemmed succulent shrub covered in sharp black spines up to half an inch long, with bright green leaves and colorful bracts that make it look like it's flowering year-round. Indoors it stays compact at under two feet, while outdoor plants in tropical climates can push six feet. What you think are petals are actually modified leaves called bracts surrounding tiny, cup-shaped flowers — a signature Euphorbia trick.

Euphorbia milii plant
Frank Vincentz, CC BY-SA 3.0, via Wikimedia Commons
Euphorbia milii plant
Frank Vincentz, CC BY-SA 3.0, via Wikimedia Commons
Care Guide

How to grow Crown-of-Thorns

Light

full sun (6 or more

Water

Allow soil to dry out

Humidity

Prefers low humidity.

Temperature

65-90°F

Soil

Fast-draining cactus or succulent mix.

Propagation

Stem tip cuttings.

Common Problems

Root rot from overwatering, spider

Did You Know

Fun Facts

The colorful 'flowers' are not flowers at all — they are bracts (modified leaves) surrounding tiny cup-shaped blooms called cyathia, a defining trait of all Euphorbias.

Pet Safety

Toxic to pets

Toxic to cats, dogs, horses, and humans. The milky white latex sap causes contact dermatitis and can temporarily damage the cornea on eye contact. Ingestion causes mouth blistering and GI irritation. All plant parts are affected. ASPCA lists it as toxic to dogs, cats, and horses.

Sources

  1. Crown of Thorns Guide - Our House Plants (opens in new tab)Reference
  2. Crown of Thorns Guide — Our House Plants (opens in new tab)Reference
  3. Crown of Thorns Plant Care - Smart Garden Guide (opens in new tab)Reference
  4. Crown of Thorns Plant Care — Smart Garden Guide (opens in new tab)Reference
  5. Euphorbia milii — NC State Extension Gardener Plant Toolbox (opens in new tab)Reference
  6. Euphorbia milii - NC State Extension Gardener Plant Toolbox (opens in new tab)University Extension
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