Crown of Thorns, Euphrobia milii

Crown of Thorns is a sun loving herbaceous, deciduous, perennial shrub. Legend has it that Euphorbia milii was the plant used as the thorny crown placed on Jesus’s head at his crucifixion. Its common name “Crown of Thorns” refers to this legend. There is evidence that this plant had been brought to the Middle East before the time of Christ and the stems are flexible enough to weave into a circle, but it is more likely that another plant was used as his crown.

Native to Madagascar, Crown of Thorns is a shrub that grows as tall as 5-6 feet. Cultivated hybrids vary in size, growth habit, and flower color. Common characteristics include 1-inch sharp grey spines, smooth-edged leaves, from 1 ½ to 6 inches long, wider near the tip (obovate) and are spirally arranged around the stem. The bright green leaves naturally drop off as the stem matures, producing a scraggly appearance on older plants. This is the form I first saw this plant. One of my students brought it in to see if we could help it become beautiful again. As we pruned it, we took stem cuttings and reproduced the plant very successfully.

Best Environment for Growing Crown of Thorns

Crown of Thorns likes a well-drained soil. Potting soil with added perlite, pumice, sharp sand, or gravel will allow the soil to drain well. It does better when the soil is allowed to dry between deep waterings. Overwatering and frequent watering will result in rotting and other fungal diseases. Any part of the plant that turns brown should be cut off immediately to prevent the rot from spreading further.

Although Crown of Thorns can be tolerant of a range of conditions, it prefers full, direct sunlight and average temperatures. It will grow in partial shade, but flowering may be reduced. It can survive temperatures down to 35°F, so it can be moved outside when temperatures allow it. It is well adapted to dry climates with low humidity.

A light fertilization early in the spring and again in the summer will be sufficient. Over fertilization can cause vigorous vegetative growth and few flowers. It is sensitive to Boron, so limit fertilizers with high levels of micronutrients.

Propagating Crown of Thorns

Always wear disposable gloves when working with Crown of Thorns. As with other plants in the Euphorbias genus, the copious, sticky, milky sap these plants produce will stick to and gum up cutting implements, so it is best to use a knife rather than shears. The milky sap can cause dermatitis and temporary blindness if it gets in your eyes, it is poisonous if ingested, so use caution when pruning or taking cuttings. Also be aware of the sharp thorns, gardening gloves worn beneath disposable gloves makes this job much easier.

If you can get past the milky sap and thick spines, the Crown of Thorns is easily propagated from prunings or stem cuttings. To make stem cuttings, remove 3-6 inches of terminal sections and dip the cut end in cold water or powdered horticultural charcoal to prevent milky sap from running excessively. Allow the cuttings to dry for 2-3 days before placing in well-drained planting mix to root. Keep the medium just barely moist, if it is too dry the cuttings will not root, but if it is too wet, they will rot. They should root in 5-8 weeks (about 2 months) when temperatures are warm.