Crown of thorns plant is the popular name for Euphorbia milii, a succulent that originates in Madagascar. It has thick fleshy stems covered in intimidating, but harmless spines. More problematic is the milky sap that exudes from broken stems; it can irritate the skin and eyes so wash it off if it gets on your hands or face. Both the stems and leaves store and conserve water, making it good choice for drought-tolerant gardens. The small, round leaves on Euphorbia milii spiral around the stem, and small flowers surrounded by brightly colored bracts appear on and off all year in mild climates. The bracts can be bright red, coral yellow or cream colored. Plants can grow up to 3 feet fall and as wide, but you can trim the plant back any time during the year.
Plant your Euphorbia milii in full sun in mild coastal areas or in partial shade in hot arid areas. The plants need fast draining and slightly gritty soil, so mix ordinary garden soil with sand, peat and some vermiculite. Water the plant well when you first plant or move it, but allow it to dry out before watering again, once the plant establishes itself. You can propagate crown of thorns from cuttings. Snap off a section of the plant's stem, and place the selection in water to stop the sap from oozing out. Remove the stem once it stops exuding sap and allow it to dry and cure in the shade for a few days. Dust the cut edge of the stem with some rooting and anti-fungal power, and then place it in moistened planting mix. The cutting will set roots in two to three weeks. Euphorbia milii is the same genus as the more famous poinsettia plant. Crown of thorns fits in well with other succulents, such as sedum and agaves as well as tender perennials annuals, such as begonias, impatiens and ornamental grasses.