Tibouchina semidecandra

The Tibouchina semidecandra, wrongly confused with the Tibouchina urvilleana, is a superb evergreen bush with an almost unreal purple flowering that blooms for several months from summer to autumn. Its flowers are larger than those of its famous cousin, and they are most often solitary. Unfortunately, this plant is not very hardy and except in the mildest areas of Europe (southern and Atlantic coast), it must be treated as an orangery plant. Therefore, it should be grown in a pot and protected from frost in winter, for example in a conservatory. In the ground, in acidic and well-drained soil, this Tibouchina will form a medium-sized bush with an exotic appearance.

The Tibouchina is a member of the Melastomataceae family, a botanical family that is largely unknown in our latitudes, but far from insignificant, as it includes nearly 180 genera and several thousand species. These plants of all types - herbaceous, bushes, trees, climbers - are widespread in tropical and subtropical areas. A few of them are used as houseplants, such as the superb Medinilla magnifica from the Philippines, with pink inflorescences several tens of centimeters long.

It was a French botanist, Jean-Baptiste Christophe Fusée-Aublet, who described the Tibouchina genus in 1775. The plant was introduced to Europe in the mid-19th century. This genus includes a very large number of species, some of which can be invasive in tropical areas. Tibouchina semidecandra is native to southeastern Brazil and mostly grows on rocky outcrops and at the edge of forests or in clearings. This species is very similar to T. urvilleana, but it is distinguished by larger and solitary flowers, rather than in clusters. It is a plant that prefers acidic soil (without limestone), rich in humus, and very well-drained.

Tibouchina semidecandra can reach 6m (20ft) in height in the tropics, but will typically reach 3m (10ft) in our gardens, with a width of around 2m. In a pot, it can be kept at 2m (7ft) or even smaller by regular pruning. In any case, it should be pruned at the end of winter to prevent it from becoming bare at the base. Similarly, if the above-ground part is damaged by frost in the ground, a severe pruning in early spring will stimulate bud growth from the base. Its ovate leaves, 5 to 10cm (2 to 4in) long, of a beautiful bright green have well-marked veins and are downy. Carried by square-sectioned stems, they give this bush a recognizable appearance. But it is its flowers that are distinctive. Solitary, 7 to 10cm (3 to 4in) in diameter, they have a sublime violet color, with decorative stamens in the shape of spider legs. The abundant flowering is renewed from week to week, from late June to October.

This Tibouchina appreciates the sun in winter, but fears its excess in summer, which is why it is easier to grow it in a pot so that it can be moved and given optimal growing conditions. In a mild enough climate, a deciduous tree providing light shade in summer will be welcome above its head. An Albizia julibrissin Summer Chocolate will be perfect in this role, and its exotic appearance will perfectly match that of the Tibouchina. The Callistemon x laevis with its red bottlebrush flowers will also be in perfect harmony, as well as the Cassia floribunda with its pure yellow flowers. To complete this exotic scene, a Caesalpinia gillesii or bird of paradise, with a fiercely tropical appearance, could be accompanied by a clump of Strelitzia reginae, the famous bird of paradise.