Bougainvilleas are plants of many mixed messages. To anyone who has visited a tropical climate, they’re the iconic plant image that’s sealed in their memories.To a nurseryman, they’re a great way to create early summer interest and sales — you just don’t walk past them without looking in admiration. And to a gardener, they can be cheery bloomers that brighten a poolside, or a source of frustration when they fail to flower as we might have expected.Let’s try to shed a little light on their history and culture, beginning with their roots. Bougainvilleas are native to tropical coastal Brazil. They were first observed in the late 1700s, and by the early 1800s, plant-hungry botanists had brought them back to Europe, where they quickly became stars in the nurseries of the time. The Royal Botanic Gardens at Kew began to distribute them worldwide to the British colonies, and the race was on.A natural hybrid with crimson bracts was discovered in a Spanish port town, and that led to discoveries of many other naturally occurring hybrids of the three species. Suddenly, there were bougainvilleas in a rainbow of brilliant colors, and in recent decades, double-flowering and variegated types have been brought into the market as well.Bougainvilleas are rambling climbers that tumble over their supports. At least, that’s how they grow in tropical areas. They’re winter-hardy only to Zone 9, which means that they can handle only very light freezes. In Texas, that relegates them to the Rio Grande Valley, the immediate Texas Gulf Coast and inland, where adventuresome gardeners as far north as San Antonio and Houston grow them outdoors. Don’t count on them to survive North Texas winters outdoors, however — not even close to it.So in our area, we use bougainvilleas either as annual flowers that we plant in late spring/early summer and bid adieu with the first freeze, or we grow them in large patio pots, so that we can overwinter them indoors in a sunroom or greenhouse. (Garages are far too dark.) They’re great companions for tropical hibiscus, sharing many of the same brilliant colors and needing the same growing conditions, both winter and summer.Bougainvilleas’ flowers are all about the same color: creamy white. What many gardeners call flowers are actually modified leaves that surround the true flowers. Botanists call them “floral bracts.” Bougainvilleas share that distinction with poinsettias, dogwoods and several other popular flowers.Gardeners’ frustration with bougainvilleas develop as plants that were bought in flower stop producing more floral bracts. That’s when it’s important to note that bougainvilleas bloom in several-week cycles. They come out of winter or summer dormant periods and start producing new leaves and stems. It’s during those bursts of vegetative growth that the plants will begin to form their bracts and buds. That assumes that the plants are getting six or eight hours of direct sunlight daily during that growth period.As the plants come into bloom, vegetative growth slows to a crawl. If the plants are given ideal lighting and ample water, they may continue to bloom for several weeks. And then it all will start over again.When I’ve grown bougainvilleas in my own landscape, I’ve found that they really bloom best when I bring them out of my greenhouse in early spring. To conserve energy and cut costs, I keep my greenhouse at 54 degrees over the winter. That’s too cool for bougainvilleas, so when they feel the warmer air of early springtime, they’re all about flowering. Then my plants typically don’t bloom much over the summer during the really hot weather, but as soon as conditions improve in early fall, they’re back into flower in September and October.I grow my bougainvilleas in large patio pots (for portability), and I give them a highly organic, lightweight potting soil. I fertilize them with a complete-and-balanced plant food in a diluted solution each time I water them. I leave them in their pots longer than I would other types of plants, because it has been my observation that bougainvillea plants that are slightly root-bound are more likely to bloom well.Bougainvilleas shut down when temperatures drop into the mid-40s. At the end of the growing season, when it’s time to bring them indoors for the winter, you’ll probably want to trim your plants. Their long, arching branches are typically covered with thorns, so they’re not the best roommates. However, trim them as little as you can get by with. They’ll need those branches when they start putting out new buds and blooms in the spring.