How to Plant, Grow, and Care for Crown of Thorns

Crown of thorns is a striking plant with an interesting history of legend and symbolism. It is a member of the Euphorbia genus, which includes such plants as the popular Poinsettia and African Milk Tree. Euphorbia is a genus of about 2,000 species that cover a wide range of physical characteristics. 

The most striking characteristic of this particular species of Euphorbia is its large, sharp spines that grow along each of its woody, succulent branches. It has historic medicinal use but is also mildly toxic if ingested. It’s a popular houseplant in the United States.

History

Crown of thorns is native to Madagascar. The genus was officially named in 1753 as part of the Euphorbiaceae Family. Legend has it this plant was used to create the crown of thorns that Roman soldiers placed on the head of Jesus Christ preceding crucifixion.  

The plant is significant in Thai culture, where its common name, Poysean, means eight saints. Some regard it as a good luck charm. It’s often kept as a potted plant and placed strategically in the home to invite positive forces. The more flowers the plant produces, the more good fortune that household is thought to receive. 

Native Area

This plant is exclusively native to the Island of Madagascar. This fascinating island is home to more than 11,000 endemic plant species, as well as 150,000 endemic species of animals.

Madagascar has five different climatic regions and is primarily subtropical. Crown of thorns grows naturally in the central region of the island. 

Characteristics

This succulent shrub displays thorns that grow from its woody branches and stems. The spiky stems are branching, water-carrying, and support bright green, fleshy leaves. The flowers are green and inconspicuous, which may come as a surprise if you’ve ever seen this plant in bloom. 

The parts of the plant commonly thought of as flowers are actually colorful and long-lasting bracts that surround the much smaller and less showy flowers. The bracts can be yellow or red and bloom in clusters at the ends of branches. As the plant ages, it drops old leaves, exposing the spiny stem.

Like all species of Euphorbia, crown of thorns contains a mildly toxic, white, milky sap that can cause skin irritation and stomach upset with ingestion. In its native environment, the plant grows to heights of five or six feet, but in cultivation, it is rarely taller than three feet and usually stays closer to two feet tall when kept in a container. 

The plant received the Award of Garden Merit from the Royal Horticultural Society for its outstanding characteristics. One of these is the exceptionally long blooming season, which can last from late winter through the following fall.

Uses

Historically, this plant has seen many medicinal uses as a painkiller, disinfectant, and antiseptic.

In the United States, the plant is most commonly kept for its ornamental value. It has a unique and beautiful appearance that makes it popular among succulent cultivators. It makes an excellent houseplant as long as it receives adequate light. 

Where to Buy

You can find this plant in many local nurseries and even at some larger hardware stores. Its ease of care and propagation has made this a popular house and garden plant. You can also find it readily through online retailers. 

Planting

Crown of thorns is an easy plant to grow. Typically started from cuttings, it can be grown indoors or out in warmer climates but needs to come indoors in the winter if you live above Zone 7. Give it plenty of sun and not too much water. 

Rock gardens and other situations where most succulent plants thrive are where this plant will perform best. It is slow growing, so it doesn’t need to be repotted often. As an outdoor plant, it is very tolerant of hot temperatures. It prefers consistent care and can become stressed with changes to the care routine. 

When this plant becomes stressed, it tends to drop its leaves. Too much sun, too much, or not enough water are all factors that stress your plant. Let’s talk more about the specific conditions this plant prefers and how to cultivate the healthiest plant possible. 

How to Grow

It doesn’t take an abundance of effort to keep one of these plants happy and thriving. As long as you consider its needs in terms of exposure, water, and temperature, your plant should reward you with a long blooming season and moderate yearly growth. 

Light

The amount of sun exposure ideal for crown of thorns will vary based on the climate in which it is grown. Whether you keep your plant indoors or out will also influence the amount and type of light the plant should receive. 

Kept indoors as a houseplant, where the temperature is consistent and mild, it can tolerate and will appreciate as much light as you can give it. Full sun is the ideal condition for this plant as long as it is kept in a temperate climate. This is where you will see the best flowering capabilities. 

When grown outdoors, this succulent still prefers plenty of sunlight, but it can get burned if it is left in the sun all day in warmer climates. In warmer climates, plant in a space that gets at least three to four hours of direct sun in the morning, with some protection in the afternoon. 

Water

As a succulent, it has lower water requirements than many plants. It is important to not overwater this plant, as its roots are sensitive to overwatering and root rot can occur easily if the roots remain wet for long periods. 

For outdoor plants, you can expect to water this plant once per week. The soil should dry between waterings to prevent fungal infection in the roots. In the summer, during times of prolonged heat and/or drought, crown of thorns will need some extra water and should be watered along with surrounding plants. 

In temperate environments, this plant will need little supplemental water and will typically thrive with normal rainfall. As a houseplant, watering should be given sparingly, allowing the soil to dry between waterings. Water this house plant about once every ten days to ensure that the roots do not remain wet for long periods. 

Soil

The most important factor when it comes to soil is drainage. The roots of this plant are very sensitive to overwatering, and wet roots will often lead to fungal rot, which will kill the plant. Ideally, outdoor soil that is a combination of loam and sand will do the best job of providing nutrients and keeping the roots of your plant happy. 

If keeping crown of thorns as a houseplant, it is best to amend your potting mix to make it drain very well. Two parts of organic potting soil, mixed with one part coarse sand or perlite, will create an environment that drains well but also retains some nutrients. Using unamended potting soil may be fine for your plant initially. If the soil retains a lot of moisture, you are likely to end up with rotten roots. 

Temperature and Humidity

Crown of thorns is native to a subtropical climate and is well suited to Zones 9-11 when grown outdoors. Ideally, this plant is happiest when temperatures stay between 65°-85°F (18-29°C), making it an excellent choice for keeping indoors where there is little fluctuation in temperature. 

This plant is very heat tolerant and can handle temperatures in the 90s as long as it has some protection from the hot afternoon sun. It is not frost tolerant, and soil temperatures below 35°F (2°C) will cause damage to the roots. The foliage may survive a light frost. However, prolonged periods of cold will be damaging. In some cases, this plant can survive colder temperatures, but it’s best not to chance it. 

It is similar to most types of cactus or succulents where moisture and humidity are concerned. This plant prefers low humidity levels and is susceptible to fungus in the presence of too much moisture in the soil or air. 

Fertilizing

These plants have relatively low fertilizer needs. Fertilizing can be carried out twice per year and only during the growing periods. The plant is dormant in winter and summer and shouldn’t be fertilized at these times as the plant’s nutrient needs are lower.

Extra fertilizer can burn the roots. Twice yearly, in spring and fall, apply a water-soluble, balanced, all-purpose fertilizer. 

Maintenance

Pruning is not necessary for growth. However, it can help maintain a pleasant form for your maturing plant. Neglecting to prune your plant can result in leggy growth and sparsity of foliage. Fortunately, the plant takes well to pruning. It is best to prune while the plant is actively growing, with the ideal time taking place in the spring to avoid removing buds. 

If your plant has become leggy with few branches, pruning can encourage branching in most Crow of Thorns plants. Take care when pruning to wear protective gloves, as the milky sap can be an irritant. Also, take care to keep this sap off of your clothes, and wash all tools before and after pruning. 

Begin pruning by removing any dead or damaged limbs and cutting back all the way to the base of the limb. Once all damaged portions of the plant are removed, consider the overall shape of the plant and what your objectives are for the future. 

It is best to avoid cutting back all leafing branches at the same time, and do not cut branches back by more than ½. Identify healthy buds on the branches that you would like to cut and trim back to just above the bud. You can also cut back to a branch joint if buds exist behind that point. Healthy buds are an indication of how and in what direction your plant will form new branches. 

As soon as new leaves appear on the new branches, it is okay to prune the remaining branches that were left after the initial pruning. You can use your cuttings to propagate the plant, as cuttings are the most effective way to propagate this plant.

Propagation

Propagate with cuttings for the highest success rate. Make sure to water your plant a day or so before taking your cuttings so that the cuttings have enough water in the stems to be most successful. Younger stems have a higher capacity to form new growth and roots, so avoid using old stems to take your cuttings. 

Trim your cuttings to about four inches long, and spray the cut ends with cool water to stop the sap from flowing. Place the cuttings on a paper towel, out of direct sun, for two to three days until the cut end callouses over. 

Prepare your potting mix by combining soil with sand or perlite to increase the drainage and moisten your mixture. Use your finger to make a shallow hole of about one and a half inches, and then dip the end of your cutting first in root hormone and then place it in the hole in your soil mix. 

Form the soil around the base of your cutting and place the container in an area that gets bright but indirect sun for a large portion of the day. Water your cutting sparingly, only enough to dampen the soil, and only when the soil is nearly dry. Your cutting will take three to four weeks to form roots. Once new growth emerges, you may commence watering as usual. 

Growing in Containers

This plant grows well in containers as long as they have proper drainage. It doesn’t like an excessive amount of space in a container, so choose a pot that is only one or two inches larger than the root ball. Excess space filled with soil can cause more water retention than the plant needs and lead to root rot. 

Your container should have proper drainage holes, and the soil needs to drain well, too. Use a mixture of soil and coarse sand or perlite to ensure that the soil doesn’t stay wet for long after watering your plant. Keeping your plant’s roots restricted in a smaller container will cause the plant to bloom more vigorously. 

Popular Varieties

Crimson Splash

	botanical name Euphorbia milii hybrid ‘Crimson Splash’
	sun requirements Full sun to partial shade
	height 2’
	hardiness zones 9-11

This exciting hybrid variety has extra large flowers and bracts with unique and beautiful coloration. The flowers appear in clusters in spring and summer.

The blooms are green, and the bracts are white with bright red ‘splashes’ of color. This easy and fast-growing variety is best known for its intense flowering habit and larger-than-usual blooms. 

Queen Millionaire

	botanical name Euphorbia milii hybrid ‘Queen Millionaire’
	sun requirements Full sun to partial shade
	height 2’
	hardiness zones 9-11

‘Queen Millionaire’ is known for having the largest flowers of any crown of thorns variety. The large, colorful bracts are coral colored with white edges and a speckled border between the two colors. This Thai hybrid will wow you with its colorful display from spring through fall. 

Golden Gem

	botanical name Euphorbia milii var. splendens ‘Golden Gem’
	sun requirements Full sun to partial shade
	height 12”-18”
	hardiness zones 10-11

‘Golden Gem’ is known for its attractive, variegated foliage. The blue-green leaves are irregularly edged with gold, making this an extra showy and attractive cultivar. This variety blooms on two-inch stems, producing smaller, bright red or yellow bracts around small, yellow flowers. 

Peppermint Candy

	botanical name Euphorbia milii hybrid ‘Peppermint Candy’
	sun requirements Full sun to partial shade
	height 12”-18”
	hardiness zones 10-11

This stunning variegated variety has a dense branching habit and wonderfully colorful and ornamental foliage. The small, red flowers bloom for nearly the entire year, only taking a short break between winter and fall before showing up again late winter to early spring. This is a slow grower and a compact plant, which makes it a great choice for keeping indoors. 

Common Problems

Pests

There are a handful of insects that may be attracted to your crown of thorns plant. Most commonly, these include spider mites, mealybugs, scales, and thrips. If you notice signs of an infestation, the first thing to do is isolate the plant away from other houseplants if indoors. 

Washing the foliage can remove some of the offending insects. Treat your plant with neem oil to eradicate the infestation, and re-treat after two weeks to ensure that all generations are eliminated.

Diseases

Fungal diseases can occur as a result of too much moisture. Crown of thorns doesn’t appreciate humidity or overwatering. Too much moisture around the foliage can promote fungus growth, and too much moisture in the soil causes fungal root rot. 

Establishing good watering habits is a must for this plant. Make sure to only water when the soil is dry to the touch, and keep your plant in soil and a container that drains freely. If you live in a humid climate, increase air circulation around your plant. 

Lack of Flowers

There are a couple of reasons why your plant isn’t flowering, and they are both sort of counterintuitive in terms of what typically makes a plant bloom. In order to flower, this plant needs a considerable amount of darkness at night, so indoor plants may receive too much light at night time to produce flowers. 

Overfertilizing can also be the cause of a lack of flowering. If your plant is growing a lot of healthy-looking, new foliage but no flowers, the culprit is likely to be an overabundance of nitrogen. Avoid fertilizing until the following spring or fall season, and use a fertilizer with less nitrogen and more phosphorus. 

Frequently Asked Questions