The purple flowers of a large, evergreen tibouchina plant (Tibouchina spp.) adorn the shrub's sprawling, vinelike branches. Native to Brazil, tibouchina plants thrive in U.S. Department of Agriculture plant hardiness zones 9b through 11, depending on the species and cultivar. The princess flower (Tibouchina urvilleana) is hardy in USDA zones 9b through 11 while glory bush (Tibouchina lepidota) is hardy in zones 10 through 11 and purple glory tree (Tibouchina granulosa) in zones 10B through 11. Taking care of a tibouchina plant is relatively basic.
Remove weeds from the tibouchina plant's garden bed. Rake a 3- to 4-inch-thick layer of mulch over the soil. Mulch inhibits weed growth, conserves water and helps maintain a consistent moisture level in the soil.
Water the tibouchina plant when its soil is dry to the touch. Generally, unless the weather is extremely hot or the plant is in a pot, watering once or twice a week with 1 inch of water is sufficient. Don't water during the rainy season when the soil is saturated. When overwatered, a tibouchina plant may develop root rot.
Apply 3 to 6 tablespoons of a granular, slow-release, balanced fertilizer, such as a 14-14-14 or 15-15-15 formula, around a tibouchina plant that is in the ground. Scratch the fertilizer into the soil's top 1 to 3 inches. Water the soil thoroughly. Fertilizer degrades at different rates, depending on the temperature. Reapply the fertilizer monthly when temperatures are above 90 degrees Fahrenheit and every three to four months when temperatures dip to 70 F. Stop fertilizing when temperatures fall below 60 F.
Fertilize a potted tibouchina plant with a liquid fertilizer formulated for flowering plants, such as a 15-30-15 formula. Mix 1/2 teaspoon of the fertilizer well with 1 gallon of water before using the solution to water the plant. Apply the solution until it drains from the pot's bottom. Fertilize the potted plant every seven to 14 days.
Prune the tibouchina plant to shape it into a mound, shrub or treelike form. Shear in late winter to reduce the plant's size. Pinch back new growth regularly to maintain the plant's shape. Although other tibouchinas may be pruned to a tree form, the purple glory tree is easiest to prune and maintain as a small tree.
Monitor the tibouchina plant for pests, such as aphids and whiteflies. A strong blast of water knocks the tiny green aphids off leaves and removes whiteflies, which are white flying insects that often are in groups. If an infestation is severe, mix 1/2 to 1 ounce of neem oil with 6 1/4 cups of water, and apply the solution in morning to all surfaces of the plant until the leaves and stems are completely coated and wet. The solution kills the bugs on contact. Reapply it every seven to 14 days as needed to control pests.