Crown of Thorns

By Lori Murray, Cameron County Master Gardener, Texas Superstar Specialist

Crown of Thorns, originally from Madagascar, does extremely well in the Valley. At one time the plants were limited to the cactus market, but now, after thirty years of breeding, they have a much wider market. The plant needs little water and blooms almost continuously throughout the year. In cooler climates it does well in containers, but here we have the luxury of planting it in our flower beds for its long flowering season.

Euphorbia milii makes a small shrub that is incredibly heat tolerant, handling full sun, high temperatures and even salt spray! It flowers in situations that would kill most annuals and perennials. In our zone, Crown of Thorns will flower into winter. Unfortunately, it will not take the kind of freeze we had in February; those that survived were usually the ones we moved indoors or were otherwise extremely well protected. Nevertheless, the plant is so striking and such a joy during the rest of the year, that it’s worth the effort required to assure its survival during our occasional cold spells.

These plants are relatives of the poinsettia, and the true flowers were originally very small. A lot of hybridizing has been done in Thailand, however, and has resulted in some species with larger flowers. Like the poinsettia, the plant’s color comes from small bracts (modified leaves which appear to be flowers but are not) surrounding small, yellowish true flowers.

It can be watered once a week (and only if dry) when it is in a growth cycle, but only once a month when dormant. It must have at least 6 hours of direct sun each day. The soil must be extremely well-drained or the roots will rot; the plant prefers to dry out between watering (a little sand in the bed can help here if the sprinkler system provides too much water.) Crown of Thorns may also be grown indoors and its hybrids bloom almost year round.

It adapts well to normal room temperatures and dry indoor environments but must be given 3 to 4 hours of direct sunlight each day. Indoors or out, keep the plant out of temperatures lower than 50 degrees. Water it from spring through late fall when the soil is dry at a depth of one inch by flooding the plant and discarding excess water that drains through. In winter, allow the plant to dry to a depth of 2 – 3 inches before watering.

Overfertilizing will keep the plant from flowering. A medium rate of slow release fertilizer is more than adequate during its blooming cycle. While it is bothered by few pests, it can be susceptible to mealy bug and white fly, so use a systemic on those planted outdoors at the first sign of either and protect them from frost and freeze.

Another name for this plant is Christ Thorn or Christ Plant. It alludes to the legend that the crown of thorns worn by Christ at the time of His crucifixion was made from the stems of this plant. (Interestingly, the stems of this plant ARE very pliable and can be woven into a circle.) There exists substantial evidence that the species, although native to Madagascar, had been brought to the Middle East before the time of Christ.

Like the poinsettia, Crown of Thorns exudes a sticky white sap called “latex” from any cut surface. The latex may produce dermatitis, much like poison ivy, and if ingested in large amounts is generally poisonous. It protects the plant from herbivores. Do not plant near fish ponds because the latex from broken roots can be fatal to fish. Crown of Thorns comes in many sizes and colors. Be sure you know what you are getting. If you wish to take a cutting from a friend’s plant, information on propagating Crown of Thorns can be found in one of the sources below.