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.
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.