Crown of Thorns.

At a glance

Care level

Easy

Plant type

Flowering succulent shrub

Light

Bright indirect light; can tolerate some direct morning sun.

Indoor light

bright-indirect

Water

Every 7 to 14 days

Mature size

Can grow up to 6 feet tall and wide, but often smaller in cultivation.

Growth rate

medium

Hardiness

USDA 10 to 12

Bloom time

Spring through fall, nearly year-round in ideal conditions

Care

Water thoroughly when the soil is dry, and ensure good drainage to prevent root rot. Provide plenty of bright light but avoid intense direct sun, which can scorch the leaves. Prune to maintain shape and encourage bushier growth.

Watering

Allow soil to dry out completely between waterings, reducing frequency in winter.

Feeding

Feed with a balanced liquid fertilizer diluted to half strength during the growing season (spring through fall).

Pruning

Prune in spring or summer to remove dead or overgrown stems and to shape the plant; wear gloves to avoid sap irritation.

Repotting

Repot every 1-2 years when root-bound, using a fresh succulent mix.

Soil

Well-draining cactus or succulent mix.

Soil pH

Slightly acidic to neutral (6.0-7.0)

Temperature

13 to 30°C

Humidity

30 to 50%

Safety

People

Toxic; causes skin irritation and gastrointestinal upset if eaten.

Pets

Toxic; can cause oral irritation, vomiting, and diarrhea.

Edibility

This plant is toxic if ingested.

How to identify it

• Thorny, scrambling stems
• Oval, fleshy green leaves
• Brightly colored bracts
• Milky white sap
• Succulent growth habit

Height

0.6 to 1.8m

Spread

0.6 to 1.8m

Leaves

Green, evergreen

Flowers

Red, Pink, Yellow, White, 0.5 to 1.5cm

Common problems

• Mealybugs — White, cottony masses on stems and leaves, sucking sap and weakening the plant.
• Spider mites — Tiny mites that cause stippling on leaves and fine webbing.
• Root rot — Caused by overwatering and poor drainage, leading to yellowing leaves and stem rot.
• Leaf drop — Can be caused by sudden changes in light, temperature, or watering.

Growing it

Propagation

Cuttings, Seed

When to plant

Spring, Summer

Since it prefers dry conditions and is toxic, companion planting is generally not recommended unless for purely aesthetic or structural purposes in a very specific xeriscape design.

Similar species

• Pencil Cactus — Both are succulents in the Euphorbia genus with a milky sap, but Pencil Cactus has cylindrical, leafless stems.
• Christmas Cactus — Both are popular houseplants that flower, but Christmas Cactus is a tropical cactus with flattened, segmented stems and no thorns.

Science

Family

Euphorbiaceae

Genus

Euphorbia

Order

Malpighiales

Class

Magnoliopsida

Native range

Madagascar

In its native habitat, it grows in dry, rocky areas and is adapted to arid conditions, relying on its succulent nature and sharp thorns for survival.

Uses

Ornamental, Houseplant

Taxonomy resolved against GBIF.

Questions people ask

Why are my Crown of Thorns leaves yellow?

Yellowing leaves can indicate overwatering, underwatering, or insufficient light.

Can I plant Crown of Thorns outdoors?

Yes, in frost-free climates (USDA zones 10-12) it can be grown outdoors in a well-draining location.

How do I get my plant to bloom more?

Ensure it receives plenty of bright, indirect light and avoid overwatering.

Is the sap dangerous?

Yes, the sap can irritate skin and eyes, and is toxic if ingested. Always wear gloves when pruning.

Where the name comes from

The common name 'Crown of Thorns' refers to the legend that this plant was used to create the crown worn by Christ during his crucifixion. The specific epithet 'milii' honors Baron Milius.

Good to know

• The milky sap is a defense mechanism to deter herbivores.
• It is believed to be one of the plants used to create Jesus's crown of thorns.
• It can be trained to grow as a small tree or a groundcover.