Crown of Thorns

Crown of Thorns

  • By Cathy Caldwell
  • /
  • November 2020-Vol.6 No. 11
  • /

As the holiday season approaches, I’m finding that, more than ever before, I’d like to avoid shopping and instead give homemade presents. Lacking any and all skills needed for crafting, I’m looking at ways to give plants, and in particular, plants I can propagate myself. My primary candidate is one you may already have: crown of thorns, which can readily be propagated with stem cuttings, though you must proceed carefully due to its thorns and because the sap can irritate the skin and eyes.

By the way, you may have other candidates for cuttings among your houseplants; one that comes to mind is Streptocarpella, which is easy to propagate using stem cuttings; read more about it in The Garden Shed, Streptocarpella, Mar. 2020. If you’re a newbie in the plant propagation department, you’ll find expert guidance in another recent article, Creating New Plants from Cuttings, Oct.2020.

Crown of thorns indoors during winter. Photo: Cathy Caldwell

But back to the crown of thorns, Euphorbia milii, also known by other common names, including Christ Thorn and Christ Plant. It seems to have more than one scientific name as well; it is sometimes referred to as Euphorbia splendens or Euphorbia milii var. splendens. It is a member of the large Euphorbiaceae (spurge) family, reportedly named for Euphorbus, an ancient Greek physician who is said to have used the sap medicinally; be aware, however, that the sticky, white sap is poisonous. Legend has it that the thorny stems were used to make the crown of thorns worn by Jesus at his crucifixion. This plant is a shrub or subshrub, and is a native of Madagascar, where it has a sprawling habit and grows as tall as 5-6 ft. In mild climates, it is grown outdoors and is a common landscape plant in southern Florida. The fact that its sap is toxic may yet turn out to be a good thing; research shows it has promise as an anti-snail toxin against the snails that are the intermediate host for the parasite (Schistosoma trematoides) that causes human schistosomiasis, a disease that is prevalent in tropical and subtropical countries.

My original crown of thorns (my Mother Plant) on the deck during summer. Photo: Cathy Caldwell

If you don’t already have a crown of thorns, I highly recommend acquiring one — preferably via a contact-free parking lot purchase. If you’re not familiar with this wonder of a plant, you’re in for a pleasant surprise. Yes, it does have sharp thorns, but few houseplants are as rewarding. For starters, it blooms almost all the time. I have the red-flowered type, and there’s nothing quite as uplifting as its profusion of blooms in mid-winter. And it continues blooming all summer when I move it out on the deck, where it has occasionally attracted hummingbirds.   A word of caution about the thorns:  be sure to place it where it is out of the way of dogs, children, and other unsuspecting passersby.

Technically, the blooms are bracts that surround the actual flowers, which are tiny and greenish. And if you want to get even more technical, the “blooms” consist of a special structure called a cyathium — which is basically bracts joined together to form a cup. The cup holds a single female flower with 3 styles surrounded by five groups of male flowers, each of which has one anther and five nectar glands. Two of those nectar glands have petal-like appendages — and those are what appear to be the “flower” to most of us.

This is not a plant that’s grown for its foliage. That’s because, as the stems mature, they tend to drop their succulent leaves. But the spiny stems themselves are intriguing, though it is not a cactus. According to some experts, it usually grows to only 2 feet as a houseplant. But give it time, and it may exceed that. My first crown of thorns — which I call my “Mother Plant” — was purchased in the 1990’s and is now three feet tall.

Pruning and Propagating

This plant, which started out as a cutting, has been pruned for a tighter growth habit. Photo: Cathy Caldwell

A crown of thorns can use regular pruning to keep it less leggy and rangy. I didn’t know this in the early years, so my Mother Plant has a wild, disorderly look that might not appeal to all. Nowadays, I do occasional pruning, and I’ve discovered how easy it is to combine that chore with propagating more plants. After my first foray into pruning, I decided to see what would happen if I planted the pruned-off stems.  I plopped those stems into a new pot and watered.  Voila! I soon had new plants after every pruning. Luck was clearly on my side since this is NOT the textbook way of propagating a crown of thorns. Here’s the correct way to proceed:

Remove 3-6″ terminal sections and dip the cut end in cold water or powdered horticultural charcoal to prevent the milky sap from running excessively. Allow the cuttings to dry for 2-3 days before placing in well-drained planting mix (such as sharp sand, perlite and peat) to root. Keep the medium just barely moist – if too dry the cuttings will not root but if too wet they may rot. They should root in 5-8 weeks when temperatures are warm.

Crown of Thorns, Euphorbia milii, Univ.Wisconsin Extension

Be sure to wear gloves — and perhaps eye protection – when you’re pruning crown of thorns.

Varieties and Hybrids

A Thai giant hybrid. Photo: cultivar413, CC BY 2.0

There does not appear to be complete agreement on the scientific name for crown of thorns.  Euphorbia milii  — the species — is typically used,  but you will also see it refered to as Euphorbia milii var. splendens, a very common variety of crown of thorns; I suspect this may very well be the plant I have. In addition to the red-flowered types, you may have seen the creamy yellow-flowered Euphorbia milii var. Tananarivae, which is sometimes sold as E. milii var. lutea. In any event, the varieties and colors available are extensive, thanks to the work of plant breeders.

The California hybrids are sometimes called the “giant crown of thorns,” — probably due to their larger flowers and stems. These include:
–‘Vulcanus’, and

A Thai hybrid is featured in the landscape at Pitzer College in southern California. Photo courtesy of John Rodman Arboretum, Pitzer Campus Plant ID Gallery

The Thai hybrids originated during the 1990’s in Thailand, and many featured larger flowers and a more upright habit than the species. But most of these hybrids have been lost. Today there are only a few growers near Bangkok that export these plants, and they have not been introduced to the nursery trade in either the US or Europe. Nevertheless, the Thai hybrids are popular as collector plants, and are available from specialty nurseries. Among these are:

–‘Jingle Bells’ (pale pink bracts tinged with red and green);
–‘New Year’ (soft yellow bracts that change to red as they age);
— ‘Pink Christmas’ (creamy bracts that develop pale pink and reddish streaks); and
–’Spring Song’ (creamy yellow bracts)

The Thai hybrid pictured at right is quite the eye-catcher.  By the way, this photo led me to the John R. Rodman Arboretum at Pitzer College, California; I highly recommend taking a look, especially if you’re interested in arid landscaping.  John R. Rodman Arboretum/Pitzer College.

The German hybrids tend to have thicker leaves and thinner stems, with flower colors of pink, red, and cream. These include ‘Somona’ (yes, that’s how it’s spelled) and ‘Gabriella’.

The Dwarf hybrids tend to be tolerant of both over- and under-watering and perform well in small containers, includes : Short and Sweet™ and ‘Mini-Bell’.

How to Grow

Crown of thorns is tough and easy-to-grow, so long as it has well-drained soil and plenty of light. It is drought tolerant and has no problem with the dry indoor air of winter. Place it in a south- or west-facing window.

Remember that leaf drop is normal. Here’s a bit of deception that is practiced by some gardeners to encourage retention of leaves on crown of thorns:  water it a bit more than strictly necessary and fertilize it occasionally (but not with a formula containing added micro-nutrients because it’s boron-sensitive). If you try this trick, be sure to watch out for root rot, and cut off any brown stems to halt the spread of rot. I haven’t tried this myself; if you do, please let me know how it works for you.

The favorable characteristics of this plant make for a long list. And it will be as happy outside in the summer as it is indoors. You may even see hummingbirds checking it out. Now that’s what I call an ideal gift.


Featured Photo:  crown of thorns (Euphorbia milii).  Photo:  Mokkie, CC BY-SA 3.0 via Wikimedia

Euphorbia milii var. splendens/Dr. Leonard Perry’s Perennial Pages/Univ. of VT

Euphorbia milii, Missouri Botanical Garden PlantFinder

Euphorbia milii Flora & Fauna Web/ Singapore Govt.

Plant of the Week/Mich.St.Univ.Beal Botanical Garden

Henry Shaw Cactus & Succulent Society


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