Full scorching sun. Spiny, woody stems are its most recognizable feature; the leaves only appear briefly, after summer rains.
Ocotillo is a not a cactus or a succulent but a very large, very spiny shrub with unbranched stems and red tubeflowers in spring. Hummingbirds are attracted to the blooms; and West Texas aficionados are invariably attracted to try their hand at growing ocotillo here at home, despite the problems of humidity and (comparatively) frequent rainfall in South Texas.
Even unrooted pieces of ocotillo will typically sprout leaves when watered. Excellent drainage and full-sun exposure will produce a better-looking plant; avoid clay soils.