Family: Lamiaceae
Common Name: Mint Bush

This genus of around 50 species of shrubs is native to Australia and is found growing naturally in a range of habitats. It belongs to the same botanical family as the common culinary herb, mint, hence the common name. The species vary in shape, size and growth habit, but all have showy, spring and summer flowers in almost every colour, from red, purple, lilac, mauve and pink through to greenish yellow, cream and white, and highly aromatic foliage, with a minty smell. The flowers are trumpet-shaped and sometimes have striped or spotted throats. The fruit is a small nut. If planted alongside paths or walkways so that the foliage is brushed when passing, they will exude a a highly aromatic scent. In garden situations, in their natural environment, they are extremely fast growing, flowering from the first year with bright displays, but often proving to be short lived, sometimes dying quite suddenly and unexpectedly. In the right situation, however, these shrubs are not necessarily short lived, with some specimens still flowering after 15 years. In the garden, the bright colours of these bushes can be used to great effect and contrast, one of the most dramatic effects being the combination of purple mint bush (P. ovalifolia) and the yellow-gold of one of the wattles (Acacia) which flower simultaneously in late spring. To enjoy this effect in climates prone to regular hard frosts, one would need to employ a cool greenhouse or conservatory. The other species would also have to be grown in a greenhouse or conservatory situation.

Species

Not all are available outside their country of origin.

P. baxteri, from Western Australia, grows to 1 m (3 ft) high, with sparse foliage and pretty, white flowers, with violet stripes in spring.

P. cuneata, alpine mint bush, a native of the mountainous areas of south-eastern Australia, grows to a height of 1 m (3 ft) and a spread of 1.5 m (5 ft). It has rounded, shiny foliage. Large, white flowers, tinged with purple, bloom profusely in early summer. This species is suitable for shady situations. Cultivar 'Alpine Gold', with brilliant yellow young leaves and gold variegated margins, is worth trying.

P. incana, velvet mint bush, spreads to a height and width of 2 m (6 ft). The small, oval leaves are soft, gray and hairy. The lavender, spring flowers have purple throats and are borne in terminal sprays. A white flowering form is also available.

P. incisa, cut leaf mint bush, is a low, compact, bushy shrub with dense, light green, fan-shaped leaves. In spring, this shrub is covered with lilac lobed flowers.

P. lasianthos, Victorian Christmas hush, is a fast-growing, tall shrub to small tree, native to cool, moist, forest habitats of eastern Australia. It has grayish green, lance-shaped, toothed leaves and creamy white flowers, tinged with pink or pale blue, and marked with purple and orange in the throats. The lovely flower sprays appear from spring through to midsummer.

P. nivea, snowy mint bush, is a large, spreading shrub with flattened, light green, aromatic leaves and a pro-fusion of white flowers, borne in sprays, in late spring. This species likes a cool, damp situation. Var. intluta, a compact type from the mountains of south-eastern New South Wales, has silvery foliage and large, bright lavender-blue flowers in late spring.

P. ovalifolia, purple mint bush, is the most commonly grown species and probably the most beautiful: it produces a spectacular, spring display of bright purple flowers. The small, oval leaves are dark green on top and grayish green on the undersides. Both the foliage and the stems are strongly aromatic. This species grows to around 2.5 m.

P. rotundifolia, purple mint bush, grows to a height of 2 m (6 ft) and a width of 1.5 m (5 ft). An abundance of purplish blue flowers covers this shrub in spring. The dense, oval, dark green leaves emit a very strong, mint perfume.

Cultivation

Under glass, grow in pots of soil-based potting compost. Provide good light and airy conditions. In the garden, if you have a suitable climate, prostantheras can be grown in a variety of soil types, but thrive in a lightly textured, well-drained soil. Newly planted specimens need care and attention until they are well established. Autumn is a good time to plant, leaving the winter months for becoming established, and spring for rapid growth.

Prostantheras generally prefer morning sun with afternoon shade, although many species tolerate light shade all day. The root systems of these plants are shallow, so planting in a sheltered position amid rocks, larger shrubs and trees is worthwhile, to prevent their being blown over in strong winds or rain. Most species will flower in the first year.

Most also benefit from regular pruning, especially straight after flowering. From the time of planting, tip pruning should be undertaken to encourage the development of a compact, bushy shape. Regular tip pruning is more effective than occasional heavy cutting, as cutting into older wood can often set back the plant severely or even kill it.

The root system of this plant is close to the surface, so avoid disturbing soil near the plant. A mulch of coarse river sand or decayed leaf mould will help reduce weeds and maintain moisture, as will the placement of large rocks around the roots.

Prostantheras can be propagated from seed or cuttings. Growing from cuttings is the easiest method for these plants, as they flower earlier and are true to type. Cuttings of side shoots taken in late spring after flowering, or in early autumn, are best. Place cuttings in a propagating case, with bottom heat and keep the compost moist at all times. Since cuttings are easy to strike, it is a good idea to have new plants always under way, especially if cultivating some of the more spectacular flowering forms.

Prostantheras will take light frosts and are fairly free from the usual insect pests and diseases, possibly due to the aromatic oils contained in the foliage. Phytophthora root rot is possibly the cause of most plant failures. This fungus thrives in warm weather, in water-logged soils.

Climate

Warmest parts of zone 9.