Native Mint Bushes (Prostanthera)

How to choose a mint bush

The Round Leaf Mint Bush is the one most gardeners know: a dense shrub to about 2 metres with small rounded leaves and mauve to purple flowers that hide the foliage in spring. The Oval Leaf Mint Bush is taller and faster, to 2 or 3 metres, with arching branches, and suits the back of a native border or an informal screen. For cold districts choose the Alpine Mint Bush, a compact high country shrub around a metre high with dark glossy leaves and white flowers marked with purple in late spring and summer. It is the frost hardy one of the group.

Among the named forms, the Mini Pink Round-leaf Mint Bush is a smaller, pink flowered selection of the round leaf species for pots and tight spots. The Poorinda Ballerina Mint Bush is one of the long grown Poorinda hybrids raised in Victoria, and the Purple Haze Rough Mint Bush is a selection of the rough mint bush, a low growing species.

Where mint bushes grow

Prostanthera is a wholly Australian genus, mostly from the forests and ranges of the south east. Mint bushes suit cool temperate and warm temperate gardens, and the tougher species cope in the subtropics on a slope or raised bed with morning sun. Humid summers with wet soil are what kill them, so they are not plants for the tropics. Most take light frost, and alpine mint bush takes heavy frost and snow. Give them sun for at least half the day, soil that drains fast and some shelter from strong wind, because the wood is brittle.

They sit naturally with other Australian native shrubs, with westringia, a relative in the mint family that is tougher on the coast, and in a garden planted for native bees.

Planting and spacing

Plant in autumn or early spring. On clay, build a mound or raised bed about 30 centimetres high rather than digging a hole that holds water. Space the round leaf and alpine species about a metre apart for an informal low hedge, the oval leaf mint bush 1.5 metres apart, and compact forms 60 to 80 centimetres apart. Mulch with coarse bark or gravel and keep it clear of the stem.

Care basics

Water through the first summer, then deeply and less often. Established plants like to dry a little between soakings, but they wilt fast in a real dry spell, so do not leave them parched in a heatwave. If you feed at all, use a low phosphorus native fertiliser in spring.

Prune lightly straight after flowering, taking back about a third of the new growth to keep the bush dense. Do not cut into old leafless wood. Mint bushes are often short lived: five to ten years is normal, and less in heavy soil or humid summers. A branch or a whole plant that collapses suddenly usually has root rot.

Common questions

How long do mint bushes live?

Usually five to ten years. Sharp drainage and a light prune each year after flowering give the longest life.

Are mint bushes frost hardy?

Most tolerate light frost. Alpine mint bush is the hardy species and handles heavy frost and snow.

When should I prune a mint bush?

Straight after the spring flowers finish. Trim the soft growth only and stay out of bare wood.

Can I grow a mint bush in a pot?

Yes. Use a free draining native potting mix and choose a compact form or the alpine mint bush.