Tropical plants often contribute brilliantly colored flowers to a home garden, and the genus Tibouchina contains several varieties that are good examples of these desirable plants. Commonly called princess or glory flowers, these specimens generally grow as evergreen shrubs or small trees in warmer parts of the U.S., but some varieties can also be container grown and overwintered indoors in colder areas.
Although all plants in this genus are called glory or princess flowers, several cultivated varieties exist with somewhat different growth habits and qualities. One plant, just called the purple glory bush (Tibouchina urvilleana), grows as a medium-sized shrub in U.S. Department of Agriculture plant hardiness zones 9 through 11. It has a rounded but somewhat sprawling growth habit and can reach a height of 6 to 8 feet with an equal width. Its leaves are fuzzy and oval with light undersides, and its flowers appear in great numbers in summer, although it also blooms sporadically year-round. Its 3-inch wide blossoms are brilliant purple, have prominent, purple stamens and open at the ends of the plant's stems.
Another variety of glory bush is sometimes called the silver-leaved princess flower (Tibouchina heteromalla) because its leaves have silky surfaces with silver overtones. This plant usually grows 4 to 6 feet tall when mature, with an equal spread, and grows in USDA zones 10 and 11. It has clusters of purple-violet flowers in flat groups called panicles in summer. Like most varieties, it grows well in either full sun or partial shade. This variety is quite sensitive to frost, but is small enough to grow in a large container and can be moved indoors to overwinter near a bright, west- or south-facing window.
One variety of glory bush (Tibouchina lipidota) is an especially compact shrub that thrives in USDA zones 10 and 11. It responds well to pruning and can be trained when young to grow as a small tree. To develop a tree-like shape, remove all but one or two main stems from a newly planted specimen and trim off any other central stems that develop during the next few years. Over time, you can raise the tree's canopy by removing any secondary stems that arise near the base of the main trunks each year. This variety has dark green leaves and an abundance of deep purple flowers in summer and fall.
One type of glory bush, sometimes called the glory tree (Tibouchina granulosa), grows naturally as a 10- to 15-foot tall tree. As the tree matures, it can become quite wide and vase-shaped. This variety grows in USDA zones 10 and 11 and has a moderate growth rate, adding 1 or 2 feet to its height each year. Its leaves are velvety and 6 inches long, and its flowers are an intense purple and flare open to a width of 2 inches. They appear from May to January as large panicles that extend well above the foliage, for an extra-showy display.