It’s spiny, really spiny. But the Euphorbia milii is a succulent, not a cactus. The plant, which is native to Madagascar and can grow up to six feet tall in the right conditions, is an excellent houseplant choice. When growing the crown of thorns, however, be sure to place it out of high-traffic areas. Like many euphorbias, the crown of thorns produces a milk-like sap that can irritate the skin. Mature plants can spread to a width of several feet, depending on pruning. And those thorns – they are about one-half-inch long and located all along the woody stems.
A Madagascar Native
This interesting succulent goes by many names. It used to be called Euphorbia splendens, and splendid seems more appropriate for this plant. But millii is in honor of Baron Milius, who introduced the plant to France in 1821. It’s also sometimes called the Christplant. The crown of thorns was introduced to the United States through Florida.
The crown of thorns is among succulents most often mistaken for a cactus. The spines don’t rise from a single areole, however, which helps differentiate spiny euphorbias from true cacti. And as a houseplant, it’s not likely to reach six feet, although we had one that grew to more than two feet before Tim trimmed it back and propagated new plants from the cuttings.
This euphorbia is only hardy as a perennial in zone 10 and higher, where it makes a fine shrub choice. It requires little watering or care, and only some warmth and sunshine to bloom almost continuously. By placing our crown of thorns in a sunny, south-facing window and giving it a summer vacation outside once temperatures warm, we’ve enjoyed blooms all year long.
The crown of thorns is a relative of the poinsettia, and original plants had deeper red flowers than those available today. New cultivars of the Euphorbia millii have smaller thorns, but what sort of a challenge is that? Most crown of thorn plants available for growing in containers are smaller than those placed in tropical landscapes, and flowers on the houseplants are only about one-half inch in diameter. But it doesn’t seem to matter; for one, the flowers appear in groupings. And I love the effect of the tiny, subtle blooms on such a thorny plant.
The crown of thorns is vulnerable to mites, mealy bugs and whiteflies. The only other problem that can occur with the easy-care succulent is overwatering. Place Euphorbia millii plants and cuttings in well-draining soil.