Euphorbia is a somewhat confusing genus, with species and subgenera frequently added and deleted. The genus includes annual, perennial, and biennial species. You’ll find herbaceous plants and woody shrub species as well as both deciduous and evergreen species. The linking characteristic among the species is the presence of a milky white sap in the plants. The species of euphorbia grown for landscape use or as houseplants are mostly succulents, which feature fascinating shapes and foliage, but a few are known for their flowers. One of the most popular euphorbia species that is not a succulent is the poinsettia. Most euphorbias bloom in the spring or summer and go dormant in the winter. In general, it’s best to plant most species in the spring after the threat of frost has passed, though houseplants typically can be started at any point. The species growth rates vary, from slow to fairly quickly. All euphorbia are toxic to humans and are toxic to dogs and cats. The level of toxicity in the plant varies from species to species. It’s critical to provide your euphorbia with very well-draining soil. Soggy soil can quickly cause root rot and kill a plant. If you’re growing your plant in a container, the pot must have ample drainage holes. An unglazed pot is best because it will allow excess moisture to escape through its walls as well as through the drainage holes. Provide your plant with lots of sunlight and periodic watering. Avoid overhead watering, which can cause powdery mildew and other fungal problems on the foliage. Pruning is typically only necessary for overgrown plants to bring them back to a manageable size.
Light
Euphorbia plants prefer full sun, meaning at least six to eight hours of direct sunlight on most days, though some species can tolerate part shade. In hot climates, some afternoon shade can be helpful for most species.
Soil
All euphorbias, especially the succulent varieties, need well-draining soil. A sandy soil with a slightly acidic to neutral soil pH between 5.0 and 7.0 is best, though most will do fine in slightly alkaline soil as well. When grown in containers, euphorbia should be planted in a cactus/succulent potting mix.
Water
From spring to fall, when the plant is actively growing, water whenever the top few inches of soil feel dry. During the winter, reduce watering to only when the plant shows signs of wilt.
Temperature and Humidity
Most euphorbia species can tolerate hot temperatures and prefer a warm environment with average daytime temperatures about 80 degrees Fahrenheit. Cold tolerance varies among the species. Some will handle a light frost while others don’t grow well in temperatures below about 55 degrees Fahrenheit. Humidity tolerance also varies. To prevent fungal diseases, it’s important for the plants to have good ventilation around them in high humidity climates.
Fertilizer
Feeding requirements vary by euphorbia species, but in general, all of them will benefit from some fertilizer. Adding compost or a balanced organic fertilizer to a new plant will help to promote healthy growth. After that initial feeding, many Euphorbia species will do fine with a weak liquid fertilizer applied throughout the growing season. For the amount to use, follow the product label instructions. Container-grown plants typically need more feeding than plants grown in the ground. And a plant that develops yellowing leaves at the bottom is one that’s in need of feeding.
Types of Euphorbia
Here are some of the most popular euphorbia species:
Cushion spurge (Euphorbia polychroma) is a clumping perennial growing 12 to 18 inches high with yellow flower bracts that appear in spring. It is grown in USDA hardiness zones 4 to 8. Crown of thorns (Euphorbia milii) is a bushy evergreen plant that can grow up to six feet tall outdoors in zones 9 to 11. It can also be grown as a houseplant but typically won’t reach its maximum size indoors. Different cultivars offer red, pink, or yellow flowers that bloom repeatedly. Baseball euphorbia (Euphorbia obesa) is a small succulent with a round, ball-shaped stem that gradually becomes cylindrical as the plant ages. It is usually grown as a houseplant but can be grown outdoors in zones 10 and 11. Donkey Tail spurge, Myrtle spurge (Euphorbia myrsinites) is an evergreen succulent with creeping, spiraled blue-green foliage. It grows six to ten inches tall and in the spring produces star-shaped yellow bracts. It makes a nice edging plant and is often used as a ground cover in zones 5 to 9. Wood spurge (Euphorbia amygdaloides) is a bushy evergreen that grows 18 to 24 inches tall with yellow flowers that appear in mid to late spring. It is suitable for growing in zones 6 to 8. Purple wood splurge (Euphorbia amygdaloides ‘Purpurea’) is a popular cultivar.
Propagating Euphorbia
Euphorbias can be grown from seed, but the seeds are difficult to germinate (or even find). Therefore, this plant is usually propagated by stem cuttings, ideally in the spring when the new growth starts but propagation can also be done in the summer.
Potting and Repotting
If you grow euphorbia as a houseplant, choose a special potting mixture blended for cacti and succulents that drains quickly. Alternatively you can also mix together three parts potting soil, three parts coarse sand or gravel, and two parts perlite or pumice. A terra cotta pot works best because the porous nature of the material wicks away moisture from the soil and helps prevent root rot.
Common Pests & Diseases
Euphorbia plants tend to be mostly problem-free. Between the milky sap and the spiky needles, few insects find euphorbias tempting. However, be on alert for a few pests. Mealybugs and spider mites are the most common pests. They will feed on the plants, weakening and eventually killing them. The population of both these insects can increase to large numbers rapidly. So catching them early is your best chance of controlling them. Insecticidal soaps and oils are good nontoxic remedies. Furthermore, root rot and fungal diseases can occur when conditions are too moist. Try to correct the plant’s growing conditions first before resorting to fungicides.
