Euphorbia is a very large genus with over 2,000 species, part of the Euphorbiaceae family whose members include surprising shapes and sizes. They can be annuals, perennials, evergreen or deciduous, even shrubs or trees. Most originated in Africa, Madagascar, and the Americas and do quite well in temperate zones worldwide including the Mediterranean climate in Sonoma County.
The common holiday plant, poinsettia, is Euphorbia pulcherrima. With showy, bright red bracts, it looks a bit different than most of its fellow species—often called spurges—grown in local gardens. Almost all are relatively easy-care perennials that are either evergreen or die down to the ground in winter and come back in the spring. Their leafy-stemmed foliage comes in many colors, sizes and textures. The genus includes many different shapes: mounds, upright stem sets or low ground crawlers, to name a few. Euphorbias tend to flower from early spring thru early summer and then continue to provide beautiful foliage throughout the growing season or even year round. Many are drought tolerant and deer and gopher resistant.
One of the more unusual aspects of Euphorbia is its blossoms. What is mistakenly called a flower is technically a cyathium, consisting of fused bracts that form a cup around a very small true flower. The bunches of leaf-like bracts grow on the end of the leafy stems and are frequently brightly colored, chartreuse in many species that reflects light and makes for a stunning display. The leafy stems are also attractive—varying from blue, blue-green, reddish-green, reddish-orange and green tinged with purple.
Planting requirements for euphorbias vary depending on the species. Many require full sun, but some can tolerate partial shade and a few can even handle full shade. Most species suitable to Sonoma County thrive in heat and can also take some frost. They can be drought tolerant, but some need regular water and almost all dislike soggy feet.
Despite the many redeeming features of euphorbias, they have some drawbacks. All have a milky white sap in their stems that is irritating on contact, can be toxic if ingested and especially painful if it gets into the eyes. It’s important to use care when cutting them and to wash up quickly after pruning. Gloves and long sleeves help protect hands and arms. The good news is that the unappetizing sap keeps the deer and gophers away. Self-sowing can also be a nuisance as is spreading by underground stems; but for most part, unwanted plants are easily pulled up.
Euphorbia amygdaloides robbiae. Commonly called Mrs. Robb’s bonnet, this species is fairly short (to 1 ft. tall) and can tolerate more shade than most euphorbias. Although the individual stems spread rapidly via rhizomes, it can be a useful variety where there is no supplemental summer irrigation—but only if it is strictly contained on all sides; otherwise, it can become an undesirable and invasive nuisance.
Euphorbia characias. This species has evergreen upright stems crowded with narrow blue-green leaves and grows in a dome shape to about 4 ft. It has brilliant chartreuse/lime green flower heads in stunning, round clusters that appear in late winter to early spring and last for many weeks. Stems should be cut back to the base as seeds form to prevent unwanted self-sowing and to allow room for new shoots that have already starting growing. E. c. wulfenii is the most commonly grown form of this species. It loves full sun and requires little water.
Euphorbia griffithii. This native of the Himalayas looks very different than the other species listed. It grows as an erect stem to 3 ft. tall and spreads slowly by creeping roots. ‘Fireglow’ has vibrant orange-red bracts that appear in early summer and create a sea of color and interest in sun or filtered light where it enjoys moderate moisture. Cut back to the ground in winter and divide every 3-4 years or more often to contain spread and keep it under control. Some gardeners prefer the similar ‘Fern Cottage’ cultivar that is said to be less invasive.
Euphorbia martinii. A hybrid of E. characias and E. amygdaloides, this perennial reaches 2-3 ft. and has dark green leaves tinged with a bit of purple. Dense clusters of chartreuse flowers with dark centers appear at branch tips in late winter to spring. It likes full sun or part shade, is drought resistant, and does not reseed as much as other species.
Euphorbia myrsinites. Commonly called myrtle spurge and donkey-tail spurge, this charming evergreen species has stems that trail on the ground octopus–like, outward from the crown. Short, chunky blue-green leaves swirl around the stems and end in clusters of chartreuse bracts in early spring and add eye-catching allure to the landscape. Rather than deadheading individual flowers, cut entire stems back to the base taking care not to remove slowly emerging replacement stems. New growth will continue year round.