Plant of the Month – Tibouchina
These South American beauties are dazzling late summer to autumn bloomers
THROUGHOUT the latter months of summer and into autumn, it’s been hard for keen gardeners not to notice the gorgeous light pink to deep purple blooms of a range of dwarf to tall shrubs from the South American genus Tibouchina in our local gardens.
While tibouchinas originate from tropical and sub-tropical South America, they have proven themselves as quite adaptable to the temperate regions of Australia and have been widely grown for years due to their dazzling displays of blooms that sometimes almost conceal the foliage beneath. Indeed, most of the popular tibouchinas grown in Australian gardens were produced by concerted breeding efforts right here in Australia.
Many of the recognisable tibouchinas seen in local gardens are varieties of the summer and autumn-flowering species Tibouchina granulosa, T. lepidota and T. urvilleana (**See note below – now Pleroma granulosum, Andesanthus lepidota and Pleroma urvilleanum). Most of these cultivars are medium to tall shrubs, ranging from 2m up to 8m in height and around 3-4 m wide.
Arguably the most well-known and widely-planted of the tibouchinas is ‘Alstonville’, a tall shrub/small tree to about 4-5m, sporting purple/violet blooms from late summer into autumn. It makes a great feature plant for a small to medium suburban garden, and in warmer areas is regarded as an ideal street tree due to its limited height.
One of the earliest tibouchinas to be seen planted in Australian gardens is T. granulosa ‘Kathleen’. Many specimens of this variety tend to grow nearly as wide as they are high, due to its propensity to produce many branching trunks from very close to ground level. ‘Kathleen’ blooms prolifically from around March to May, with stunning mauve-pink flowers borne all over the rounded crown. Growing to 5m high and nearly as wide, ‘Kathleen’ is suited to medium to large gardens.
By their very nature, the cultivars of Tibouchina mutabilis (** See note below – now Pleroma mutabile), derived from ‘mutare’, Latin for “to change”, bear flowers that slowly change colour as they mature. A very popular variety of this species is ‘Noelene’, a densely-foliaged large shrub growing to about 5m high and 3m wide. ‘Noelene’ will flower from late spring to early summer, its blooms starting out almost white, then ageing to rose-pink and finally a reddish-violet.
For smaller gardens, one of the earliest and most successful dwarf cultivars was Tibouchina ‘Jules’, growing to about 1m high and somewhat wider, sporting a profusion of violet-purple blooms about 56cm in diameter from March to May. ‘Jules’ proved to be a very successful plant when grown in containers.
No doubt one of the most exciting developments in the breeding of tibouchinas in Australia began around 1995, when Terry Keogh, an avocado grower in Queensland, began an active breeding program dedicated to producing native and exotic plants of manageable sizes for home gardens.
Terry became fascinated with tibouchinas due to their ability to “make a statement” in the landscape. Breeding new cultivars wasn’t easy, due to their reluctance to release pollen unless the stamens were vibrated at a specific frequency similar to the wing beats of their native South American pollinator, the hummingbird!
As a result of Terry’s breeding program, a wonderful range of dwarf ‘Baby’ tibouchinas, from the Fantasy Flower range, were “born”.
Both ‘Cool Baby’ (large pink and white flowers with pink margins) and ‘Groovy Baby’ (large electric purple flowers) will only grow to 45cm H and 45cm W. Both plants are so floriferous that the flowers will usually cover the plant and hide the foliage. They are long-flowering, producing blooms right through the warmer months. They are well suited to pot culture.
Others in the ‘Baby’ range are ‘Peace Baby’ (clear white flowers, 60cm H and 80cm W), and ‘Foxxy Baby’ (1m H x 1m W, pale white/pink flowers).
As tibouchinas hail from the upper altitudes of warmer climates, they can be a little delicate if exposed to frosts when first planted. Find a warm, sunny position in your garden for these beauties. Of course, the smaller varieties can be moved to warmer spots if planted in containers.
Tibouchinas prefer acidic soils (pH 5 – 7) so add some sulphur if your soil is alkaline. They can tolerate a range of soil textures, but it’s best if they’re planted in a wellstructured soil, so ensure the site is wellprepared with composts and other organic matter.
Ensure your tibouchinas are kept moist by mulching around the base and beyond the drip-line by about 50cm.
The taller tibouchinas will require regular pruning to keep them bushy and flowering well. Best time to prune is late winter. A light pruning of the current year’s wood is all that is needed to ensure dense, twiggy growth. Don’t prune unless you’re convinced all frosts have finished. Planting is best done in early summer.
Check your quality local nurseries for these great plants now.
** Note: In 2019, the genus Tibouchina was reassigned into several separate genera. Some species stayed in Tibouchina, with many of our garden species and their cultivars moving to Pleroma and Andesanthus. Most nursery plant tags will continue to list Tibouchina as the genus at this stage, as I have done in this article as well.