Crown of thorns (Euphorbia milii) is a pretty succulent plant that can bloom almost all year round, even indoors. The thick, bright green leaves grow along new stem growth, but watch out for thorns. The true flowers are small and green, surrounded by showy bracts in red, orange, pink, yellow or white. This slow-growing plant grows into a shrub outdoors that reaches 3 to 6 feet in height. As a houseplant, you can expect it to only grow to around 60cm tall. Euphorbia is poisonous to humans and pets.
Crown of Thorns Care
Although the crown of thorns can grow into a woody shrub, it is also an ideal houseplant for most homes. It likes the same room temperature that humans enjoy and can cope with the lack of humidity found in most homes during the winter. Crown of thorns is perennial only in USDA hardiness zones 9, 10 and 11. In colder climates it is often grown as a houseplant. If you are growing it outdoors, give the plant enough space. The crown of thorns is ideal as a solitary plant. At the end of the season, perform a renewal pruning and cut off any older, fading leaves to encourage new growth.
Container-grown crown of thorns can spend the summer anywhere you need color or interest. Be sure to bring it indoors before nighttime temperatures drop below 50 degrees Fahrenheit. Of course, you can keep your crown of thorns indoors all year round. A bright window will cheer you up at any time of the year.
The crown of thorns blooms repeatedly throughout the year. The actual flowers are the insignificant green centers, but they are surrounded by showy bracts that look like colorful petals. Despite the thorns, the crown of thorns is easy to handle by grasping it by the petioles or holding on to the roots.
As with most flowering plants, the better the sun exposure, the more flowers you will get. Euphorbia requires direct sunlight and will bloom reliably as long as it receives at least three to four hours of bright sunlight daily. Try placing them outdoors in full sun. Place your indoor plant in a west or south facing location during winter.
If growing outdoors, plant them in well-drained soil and full sun. In dry climates, plants enjoy some midday shade for better flowering. The crown of thorns is a very adaptable houseplant. It requires well-draining cactus potting soil and should not be planted in a container that is more than an inch or two larger than the root ball. If there is too much soil, it will retain water and can lead to root rot.
Since it is a succulent, the crown of thorns is very water tolerant. Water when the soil feels dry about an inch below the surface. Water thoroughly and allow excess water to drain. Do not leave your plant in water or wet soil for long periods of time, otherwise the roots will rot. The crown of thorns goes into a semi-dormant phase in winter and requires less frequent watering and no feed.
Temperature and humidity
At least half a day of sunlight is a basic requirement for the crown of thorns. Temperature-wise, a comfortable 65 to 75 degrees Fahrenheit is good. Don’t worry if you turn down the thermostat at night. The crown of thorns can tolerate temperatures up to 50 degrees Fahrenheit.
Feed your crown of thorns with a balanced houseplant fertilizer from spring to fall. You can do this every other watering if you dilute the fertilizer to half strength.