How to Grow and Care for Crown of Thorns

Crown of thorns plant with red flowers with thick bright green leaves

The Spruce / Gyscha Rendy

Crown of thorns (Euphorbia milii) is a pretty succulent plant that can bloom almost year-round, even indoors. The thick, bright green leaves grow along the new stem growth, but watch out for thorns. The true flowers are small and green, surrounded by showy bracts in red, orange, pink, yellow, or white. This slow-growing plant will grow into a shrub reaching 3 to 6 feet tall outdoors. As a houseplant, expect it to reach only about 2 feet in height. Euphorbia is poisonous to humans and pets.

Common Name Crown of thorns, crown-of-thorns, Christ plant, Christ thorn
Botanical Name  Euphorbia milii
Family Euphorbiaceae
Plant Type Succulent 
Mature Size 3-6 ft. tall outdoors, 2 ft. tall indoors
Sun Exposure Full, partial 
Soil Type Well-drained
Soil pH Neutral to acidic
Bloom Time  Spring, summer, fall, winter
Flower Color  Red, orange, pink, yellow, or white
Hardiness Zones  9-11 (USDA)
Native Area  Africa
Toxicity  Toxic to people and pets

Crown of Thorns Care

Although crown of thorns can grow into a woody shrub, it is also an ideal houseplant for most homes. It likes the same room temperature that people enjoy and it can handle the lack of humidity prevalent in most homes during the winter. Crown of thorns is only perennial in USDA Hardiness Zones 9, 10, and 11. In colder climates, it is often grown as a houseplant. If growing it outdoors, give the plant plenty of room. Crown of thorns makes an excellent specimen plant. Give it some renewal pruning at the end of the season, cutting away any older, fading leaves to encourage new growth.

Container-grown crown of thorns can spend the summer outdoors wherever you need color or interest. Be sure to bring it inside before nighttime temperatures dip below 50 degrees Fahrenheit. Of course, you can keep your crown of thorns indoors all year. In a bright window, it will perk up any season.

Crown of thorns will repeat bloom throughout the year. The actual flowers are the insignificant green centers, but they are surrounded by showy bracts that look like colorful petals. Despite its thorns, crown of thorns is easy to handle if you grab it by its leafy stems or hold it by its roots.

Light

As with most flowering plants, the better the sun exposure, the more blooms you will get. Euphorbia needs direct sunlight and it will reliably bloom as long as it receives at least three to four hours of bright sunlight per day. Outdoors, try to place it under full sun. Indoors, place your plant in a west or south-facing spot during winter.

Soil

If growing outdoors, plant in well-draining soil and full sun. In dry climates, the plants will appreciate some mid-day shade for better blooms. Crown of thorns is a very adaptable houseplant. It needs a well-draining cactus potting mix and should not be planted in a container that is more than an inch or two larger than the root ball. If there is excess soil, it will retain water and could cause the roots to rot. 

Water

Since it is a succulent, crown of thorns is very forgiving about water. Water when the soil feels dry about 1 inch below the surface. Water thoroughly and allow any excess to drain off. Do not let your plant sit in water or wet soil for prolonged periods of time or the roots will rot. Crown of thorns will go semi-dormant in the winter and need less frequent watering and no food.

Temperature and Humidity

At least half a day of sunlight is a major requirement for crown of thorns. Temperature-wise, a comfortable 65 to 75 degrees Fahrenheit is good. Don’t worry if you lower the thermostat at night; crown of thorns can handle temperatures down to 50 degrees Fahrenheit.

Fertilizer

From spring through fall, feed your crown of thorns with a balanced houseplant fertilizer. You can do this every other time you water if you dilute the fertilizer to half strength.

Crown of thorns plant red flowers and thorns on single stem
The Spruce / Gyscha Rendy
Crown of thorn plant with stems of thorns and bright green leaves
The Spruce / Gyscha Rendy
Crown of thorn plants with thorns on stems and red flowers
The Spruce / Gyscha Rendy
Crown of thorn shrub with woody stems and red flowers with yellow centers
The Spruce / Gyscha Rendy
Crown of thorns branch with red flowers and leaves closeup
The Spruce / Gyscha Rendy

Types of Crown of Thorns

Hybridizers continue to come out with flashy new varieties. Look for a plant that is in bloom, so you will know exactly what you are getting. Local nurseries generally only carry a few varieties and mail-order catalogs are a good place to look for unusual hybrids. Here are some types of Euphorbia milii to try:

  • 'Brush Fire': Thick, fleshy leaves and bright red flowers
  • 'Creme Supreme': Strappy leaves and creamy white flowers
  • 'Short and Sweet': Red flowers (dwarf, reaching 12 to 18 inches tall)
  • 'Maxi Zephyr': Apricot colored bell-shaped blooms
  • 'Maxi Pink Cadillac': Coral-pink blooms
  • 'Red Gundula': Pinkish-red blooms
  • 'Splendens': Red blooms but grows tall to 5 or 6 feet
  • California hybrids are bred for thick stems and large flowers. They are sometimes labeled Giant Crown of Thorns. Two good cultivars to grow outdoors are 'Rosalie' and 'Saturnus.'

Pruning

Crown of thorns may become leggy if you do not prune it to encourage leafy or branching growth. You will also want to prune crown of thorns to keep a compact shape if it's a houseplant. Avoid lopping off healthy buds. When pruning this plant, whether indoors or outdoors, protect your eyes, hands, and skin from the sap. To stop sap from flowing, spray water directly on the wound.

Propagating Crown of Thorns

Most modern crown of thorns are hybrids and are not started from seed. However, they are easy to propagate from tip cuttings. To limit the amount of sap you come in contact with, wear gloves and dip each cutting into warm water, letting them sit in it for a couple of minutes. Then lay them out to dry and callus over for a few days before planting.

Potting and Repotting Crown of Thorns

A crown of thorns houseplant is simple to repot every two or so years. Be sure to wear protective gloves and eye gear while potting your plant. Remove the plant from its current pot, loosen the roots, and place it in a new pot that's a couple of inches larger in diameter. Use cactus potting mix only. Water thoroughly after you have placed the plant in its new home.

Common Pests & Plant Diseases

Most pests steer clear of the plant; however, common houseplant pests, such as scale, mealybug, and thrips may be a problem.

Watch for fungal diseases such as botrytis, leaf spotting disease, as well as root rot, even if the plant is indoors. Allowing the soil to dry before watering again will help avoid these problems.

Common Problems With Crown of Thorns

Although this is a tough plant and easy to grow, you may encounter a couple of problems with crown of thorns that can usually be remedied.

Yellowing Leaves

Crown of thorn's leaves should be bright green. If the leaves are yellowing and beginning to shrivel, it could mean the plant is underwatered. It could also mean the plant is not doing well because of sudden temperature changes, which is especially common with houseplants. Poor soil quality or the wrong type of mix could also be turning leaves yellow.

Dropping Leaves

Some cyclical leaf drop is normal, especially before winter when the plant rests. However, if the plant is completely stressed due to living in an environment that's too hot or it's being underwatered, it will shed every leaf. When the source of the stress is eliminated the leaves will begin to grow back.

Lack of Blooms

If your indoor crown of thorns is not blooming, it may be getting too much light at night (they need total nighttime darkness for best flowering conditions). Poor flowering may also be the result of overfertilizing. Too much fertilizer will produce more foliage than flowers.

Browning Stems or Leaves

Immediately cut off and dispose of any brown parts of your crown of thorns. Brown portions may mean a fungus developed due to prolonged moisture (indoors or outdoors) which rotted parts of the plant.

FAQ
  • Is Euphorbia milii a cactus?

    The succulent, crown of thorns, is not a cactus. It is considered to look cactus-like because it's a spiny shrub.

  • Are there medicinal benefits of the crown of thorns plant?

    No, because Euphorbia milii is different than other types of Euphorbia (such as Euphorbia hirta) which are non-succulent herbs included in the very broad Euphorbiaceae family. The herbs may be used for medicinal purposes.

  • Is the crown of thorns a good luck plant?

    There are many stories about this plant's luck potential. The plant's name is derived from the belief by some that the crown of thorns worn by Jesus Christ at his crucifixion was made from stems of this plant. For this reason, various cultures around the world think of this as a good luck plant. In Thailand, the plant is considered lucky because an auspicious eight flowers grows per stem, which represents eight saints of Chinese mythology.

Article Sources
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  1. Crown of Thorns, Euphorbia milii. Wisconsin Horticulture.

  2. Crown of thorns. Pet Poison Helpline.

  3. Euphorbia milii. Henry Shaw Cactus and Succulent Society.