Azul Lady Slipper

The slipper plant grows as a clump of slender, mostly leafless stems. Each stem is about half an inch thick and tapers toward the tip like a candle. In ‘Azul’, a thicker waxy coating covers those stems, and it gives them a soft blue-gray color instead of the lime-green of typical plants. That waxy layer is called candelilla, meaning little candle, and it adds a faint sheen. New stems push up from underground runners, so a single plant slowly widens into a dense, upright clump. Young plants stand stiff and vertical. As the stems lengthen and gain weight, they begin to arch and lean, and older clumps often sprawl. ‘Azul’ grows more slowly than the green form, so it holds its neat shape longer. In cool weather, the stems may flush red. This is a normal response to winter chill, not a sign of trouble.

This succulent comes from the Sonoran Desert of northwestern Mexico. There it grows on sandy plains and rocky hillsides among creosote and other dry-country shrubs. Those roots explain its comfort with strong heat, bright light, and long dry spells once established. Light also shapes the plant: in full sun, the stems stay short and upright. In shade they stretch, loop, and sprawl. In the hottest low-desert gardens, harsh reflected sun can yellow the stems, so a little afternoon shade keeps their color. From summer into fall, small orange-red structures shaped like slippers open at the stem tips. Their color and narrow shape are matched to hummingbirds, which reach in for nectar and pollinate the plant as they feed. This plant needs fast-draining soil and only occasional deep watering in summer. Protect it where winter lows fall below the mid-20s.

Like all members of the genus Euphorbia, the slipper plant does not bloom the way most flowers do. What looks like one slipper is actually a cyathium. This is a tight cluster of much-reduced male and female flowers around a central nectar gland. Such structures are a signature of the spurge family. The plant also has a tangled name history. It was long known as Pedilanthus macrocarpus. When the genus Pedilanthus was folded into Euphorbia in the early 2000s, the name Euphorbia macrocarpa was already taken. So botanist Victor Steinmann renamed it Euphorbia lomelii, honoring Mexican botanist José Lomelí. One caution is worth noting. Like other spurges, the stems hold a milky sap that can irritate skin and eyes. Wear gloves when pruning, keep the sap from your face, and wash after handling.