What most folks believe are colorful flowers on the Euphorbia milii are actually bracts. The tiny center portion is the actual flower. No matter, this succulent from Madagascar is a popular houseplant throughout the world. It is easy to grow and the bracts/flowers are available in many colors. (Its relative, the E. pulcherrima has the same bract/flower structure. Most everyone knows that plant by its common name—the Poinsettia.) The common name for E. milii is Crown of Thorns, for good reason. The stem has many sharp thorns that can puncture skin.
I keep my potted E. milii under the covered patio in the summer. The leaves don’t do well in full sun, so it doesn’t make a good landscape plant in this area. Since I water it all summer, it keeps its leaves, and will occasionally flower, but most flowering occurs during mild winters. If I withheld water, it would become dormant and actually look like a dead stem. Once watered, it grows leaves and begins to flower. There is a limit to this treatment—withhold water too long and it really will be a dead stem.
The plant in the photo started as a cutting from a large plant that succumbed to the hard freeze this past winter. I trimmed that plant in late summer last year and planted several of the cuttings. All are doing well. This is one of the easiest plants to propagate—rivaled only by oleander.
As with all Euphorbia species, the sap is poisonous and can be very irritating, especially if it gets in the eyes. My husband got some Euphorbia sap in his eyes last year and spent several painful hours in the Emergency room having his eyes irrigated. He then had to take pain medication and use an antibiotic ointment in them for several days to prevent infection, which apparently is a common occurrence with Euphorbia sap.