Euphorbia species include a vast list of annuals, biennials, perennials, succulents and evergreens. Plants produce a variety of foliage depending on the type of plant; however, all Euphorbias contain a milky sap that irritates skin on contact and is toxic if ingested, so keep children or pets away from cut flowers that bleed sap. Euphorbias do not produce true flowers; instead, they produce a cyathium, which is actually a unisexual flower cluster.
Annual and Biennial
Annual and biennial Euphorbias are most often grown as annuals. They are grown for their foliage that ranges from green and red to green and white. These shrubby Euphorbias grow 18 to 36 inches tall and thrive in warm temperatures. Plants require full sun to partial shade and well-drained soil. You can grow them from seed and they readily self-seed. Snow-on-the-mountain (Euphorbia marginata) is commonly grown as annual but is hardy in U.S. Department of Agriculture plant hardiness zones 2 through 11. Plants produce green oval, light green foliage striped with white. Variegated green and white flowers appear in summer.
Perennial Euphorbias are grown for their colorful bracts that surround insignificant flowers and strong horizontal foliage. Plants range from 6 to 36 inches tall and make excellent edging and border plants for rock gardens. Perennial Euphorbias require full sun to partial shade and thrive in average to poor soil. Flowering times vary by plant. The perennial cushion spurge (E. polychroma) produces deep-green leaves arranged on hairy stems. Rounded clusters of bright yellow flowers surrounded by yellow bracts appear in spring to midsummer in USDA zones 5 through 10.
Perennial Euphorbias include evergreen varieties. Mediterranean spurge (E. characias "Wulfenii") grows in USDA plant hardiness zones 7 though 10 and is a common evergreen Euphorbia grown for its evergreen upright stems crowded with blue-green foliage. This shrubby evergreen grows in a dome shape reaching 4 feet tall and wide. Lime-green flowers in dense cylindrical clusters appear in late winter. When stalks fade and turn yellow, cut them to the ground to make way for the new shoots already forming for next year's growth.
Succulent Euphorbias grow outdoors in the warmest climates with a temperature at least 55 degrees Fahrenheit and require care similar to that of the cactus family. The crown of thorns (E. milii formerly E. splendens) is a climbing succulent that grows in USDA plant hardiness zones 9b through 11. The plant has long, slender branches with tough spines and produces bright red flowers. Crown of thorns has a spreading growth habit makes an excellent ground cover or climbing on a wall.