We buy bougainvilleas in the spring, usually when they’re full of buds and floral bracts. By mid-summer, however, they seem to stall out. "Why isn’t my bougainvillea blooming?" is gardeners’ most common question.
Granted, bougainvilleas are of tropical origins, but not all tropical climates are as hot as Texas. Bougainvilleas seem to bloom best at more moderate temperatures, say in the 65-90 F. range. That’s why they bloom more frequently here in the spring and the fall.
They also flower better if they’re kept just a little bit root-bound. That assumes, of course, that you’re growing yours in a container. Keep it moist at all times to protect the existing foliage from drought, but avoid excessive levels of nitrogen that might stimulate too much new leaf growth.
(Did you know that the showy parts of a bougainvillea are actually its floral "bracts" – modified leaves? The actual flowers are the tubular, white parts in the centers of the bracts.)