Sometimes known as glory bushes, Tibouchina lepidota (previously called Lasiandra) begin show their big sumptuous purple flowers in March or April and these continue all through autumn and sometimes into early winter in Sydney. The most commonly seen cultivar is Tibouchina lepidota 'Alstonville', which throbs with opulent colour when back-lit by the autumnal sun. They open from attractive reddish buds and have curled stamens like claws. These plants became popular about fifteen or twenty years ago and so there are many mature specimens to be seen around nowadays, decorating streetscapes and gardens: Sydney seems to have the perfect climate for them, as it does for many South American plants.
They can be shaped as small trees by training to a single trunk, which is what I have now done with my new one, due to pure laziness, after years of cutting back very heavily in late winter so that the shrub would stay around 3 m in height. I am not sure how high it will go left unpruned - apparently they sometimes can get to 12 m, though 5 m seems to be the usual height! Anyway, at the moment it fits in well to my semitropical-style garden, and its large veined leaves provide welcome background greenery in every season. Tibouchina can be grown in many tasteful planting schemes of pinks, white, blues and other purples, such as with Camellia sasanqua, crepe myrtles, Salvia (especially some of the tall-growing autumn-flowering ones) , and Brugmansia. True drama can be achieved by pairing the purple flowers with some of the brilliant orange or red blooms of autumn, such as Canna and Dahlia, the bird-like blooms of Strelitzia or red Pentas. They also look stunning grown against a background of autumn-colouring trees or near autumn-berrying trees or shrubs. Tibouchina flowers are also striking when paired with the foliage of red Iresine herbstii 'Brilliantissima', which glows like exotic cellophane, or the burgundy chenille tassels of annual Amaranthus caudatus, which achieves shrub-like stature by autumn.
These plants may be difficult to establish in areas with very frosty winters, unless given protection in their early years and/or planted against a sunny wall. They enjoy a sunny position (flowering will be sparse in a shady spot and the growth habit will be lanky), and like a soil with organic matter incorporated in at the time of planting. Regular moisture will help them to establish - after a while, they are fairly drought tolerant; if summers are very dry, they will appreciate some moisture every so often. Pruning will depend on whether you want a shrub or tree shape - but even if you are training your Tibouchina into a tree, light pruning around August of the spent flower-heads will be beneficial. If you decide your specimen is just too tall, you can prune it very hard at that time and it will recover! This can be done in stages to reduce the shock on the plant. They can be propagated by cuttings in late spring and summer.