Crown of thorns (Euphorbia milii; formerly E. splendens) are hardy shrubs that feature attractive, brightly colored bracts. The plant also features large, 1-inch thorns and poisonous sap, according to the University of Florida. The largest cultivars can reach widths and heights of 5 feet. Often grown as a houseplant, some cultivars of this plant, which is native to Madagascar, also work well as as a groundcover. Crown of thorns grows especially well in coastal areas, as it can tolerate sandy soil and salty conditions. Care of this plant does not go beyond basic culture.
Choose a location that is exposed to either full sun or partial shade. Most varieties of the plant grow best in full sunlight, which is defined as a minimum of 6 hours of sun exposure per day.
Plant the crown of thorns in well-draining soil that is loose and loamy or sandy. Heavy clay soil should be amended with perlite or sand to aid in drainage.
Water when the surface of the soil becomes dry to the touch during the growing season (spring through summer), and even less often during the winter. Although this plant can tolerate a wide variety of environmental conditions, the one thing it does not handle well is overwatering, according to the University of Florida. Overwatering will cause root rot to develop, which is a fungal disease that destroys the roots of the plant.
Keep the plant warm, especially if it is indoors. Do not place it by any cold or hot drafts. Daytime temperatures in the low 80s F, with a drop by 15 to 20 degrees at night, are recommended by Michigan State University.
Fertilize only lightly with a balanced (10-10-10), water-soluble fertilizer in early spring. Use a dose half that recommended on the label for the size of your plant. These shrubs also do not tolerate overfertilization.
Prune off damaged or dead branches in early spring. Take care to avoid the sharp thorns and poisonous sap.