All About the Crown of Thorns, a Unique and Easy Houseplant

The Crown of Thorns, or Euphorbia milii, is a fairytale-like plant that grows into shrubs of thorned branches with lovely green leaves and brightly colored blooms.

It is a hardy plant that can tolerate neglect and a wide range of conditions, which makes it a wonderful houseplant for a sunny window.

Today we will talk about where Crown of Thorns grows in the wild, how it became a popular houseplant, what varieties are available, how to care for it, and more!

Table of Contents

Where does the Crown of Thorns grow natively?

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Crown of Thorns / Euphorbia milii, Photo by: kenbehrens, iNaturalist, Source

The Crown of Thorns, or Euphorbia milii, is native to Madagascar.

It grows in a shrub-like manner with woody stems covered in thorns. It also develops colorful, flower-like structures called brachts, which are modified leaves. In the center of the brachts forms the actual flower, tiny in comparison, to the colorful petal-like structures around it.

Here’s a close-up photo of Crown of Thorns Flowers first and then Euphorbia obesa’s flowers second. You can see the resemblance!

1280px Euphorbia Milii flowers
Euphorbia Milii flowers, Photo by: Ezra Katz, Wikipedia, Source

What is the Crown of Thorns’ history as a houseplant?

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The beautiful Crown of Thorns, Euphorbia milii was discovered by M. le baren
Milius about 1821 on the island of Madagascar, located off Africa’s southeast coast.

This shrub was first described in 1826 by Charles Robert Alexandre Des Moulins
(1798–1875) and named in honor of Milius (species name milii).

Milius was a French governor and administrator on the island of Reunion, a part of the Mascarene Island
group about 400 miles east of Madagascar

W. J. Beal Botanical Garden, Crown-of-Thorns, Source

Crown of Thorns was discovered in the early 1800’s and introduced into cultivation at the same time.

It has been grown inside and out around the world and has become invasive in some areas due to its hardy nature.

What varieties of Crown of Thorns are there?

In the past 50 ish years, Euphorbia milii has been hybridized many times to produce plants with larger leaves and flowers, plants with variegated foliage, and plants with a wide range of bract and floral colors and combinations.

The most common varieties in cultivation are plants with red, pink, yellow, or white brachts and plants with outer variegation on the leaves.

However, there are hundreds of varieties beyond these. I will include a photo below showing just a small selection of the huge range out there.

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How do you care for a Crown of Thorns?

Crown of Thorns Care Summary

In-depth care is below this chart

Humidity:Normal household humidity levels
Light:Provide as much light as possible
Pot:Any pot with a drainage hole and snug fit
Potting Mix:A very well-draining mix
Water:Water when dry; do not keep wet
Fertilizer:Fertilize lightly during active growth

How much light does Crown of Thorns need?

Crown of Thorns will be pleased with as much light as you can provide for it. While it can be okay with just a couple hours of direct sun each day, it will happily soak up full sun all day.

The more sun you can provide, the more growth, foliage, and blooms you are likely to see.

What kind of planter and potting mix does Crown of Thorns prefer?

This plant really needs lots of good drainage, which means a pot with drainage holes and a potting mix with lots of stuff in it that will allow the water to pass through quickly.

A mix of 50/50 potting mix to perlite could work well. Or you could add horticultural sand or pumice also, either as a replacement for perlite or in addition to perlite.

As for planters, terracotta is a great choice since it helps to absorb some of the moisture sitting in the potting mix, but really any pot with adequate drainage holes will be fine.

When does Crown of Thorns need to be watered?

Crown of Thorns only wants to be watered when its pot is completely dry from top to bottom.

The easiest way to judge this (in my opinion) is to have your Crown of Thorns in a terracotta pot or a plastic nursery pot where it becomes noticeably lighter when dry and much heavier when saturated.

You can also use your finger, a moisture meter, or a chopstick to help.

You’ll want to stick a chopstick or moisture meter as far down into the pot as possible.

If the chopstick removes clean, it is dry. If it removes with some moist soil stuck to it, it is still wet.

The moisture meter should read a 2 or 1 before watering.

If using your finger, insert it as deeply into the potting mix as possible and only water when the potting mix feels dry.

How do you fertilize Crown of Thorns?

Crown of Thorns does best when fertilized every few weeks during active growth. This will ensure it continues to support the growth of healthy foliage and gorgeous bracts and flowers.

This plant, like most arid plants, prefers a succulent fertilizer or a very diluted, well-balanced fertilizer.

How do you get a Crown of Thorns to bloom again?

If your Crown of Thorns hasn’t bloomed for a long time, it may need an increase in light and/or fertilizer. Euphorbia milii can grow well even in direct sun, so providing this plant with lots of light is one key to success. It also needs regular watering (when it’s completely dry) and occasional fertilizing to be in optimum health.

Adjusting any or all of these characteristics should help to bring your plant to bloom.

Once your plant is starting to bloom:

When flowers and bracts begin to grow, they often appear lighter in color at first and then darken.

I believe the intensity of the color is affected by the amount of light the plant is getting, but this is my own anecdotal experience and not necessarily a fact.

Is the Crown of Thorns toxic?

Yes, Crown of Thorns is very toxic.

Being part of the Euphorbia family, it is known for having a white latex sap that can be super irritating to skin, very harmful to our eyes, and incredibly toxic to ingest.

For this reason, Euphorbias, like the Crown of Thorns, should live somewhere that kids and pets cannot access.

What are some common issues when growing a Crown of Thorns?

Leaf drop

Leaf drop can happen when you first bring the plant home and it is adjusting to your new space.

It can also happen over time if the plant is overwatered, underwatered, or suffering from spider mites.

Root rot

This plant is very prone to root rot. It is not used to tolerating wet conditions for any length of time. Be sure to only water this plant when completely dry and ensure it is in a very well-draining potting mix.

Spider mites, mealybugs, and whiteflies

While these plants aren’t super pest prone, they can get a few of the common household pests like spider mites, mealybugs, and whiteflies.

If you think you might be dealing with pests, click here to identify what pest it is and what you can do about it.

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