Prostanthera askania

Tranquility Mintbush

Family: Lamiaceae

An erect to spreading (sometimes scrambling) open-branched shrub that grows to 3 metres high by up to 1 metre wide.

It is found in moist sclerophyll forest and warm temperate rainforest communities, and the ecotone between them. It has a very restricted geographic range, in the central coast subdivision of NSW, found on the upper reaches of creeks that flow into Tuggerah Lake and Brisbane Waters, within the Wyong and Gosford local government areas. A new and very small population was found in Bouddi National Park, at Macmasters Beach, in the last 20 years.

It is listed as threatened with extinction in the wild.

Prostanthera have simple, opposite and usually odorous leaves (a typical Lamiaceae feature). In this species, leaves are strongly aromatic, to 40 mm long and to 25 mm wide, dull green and are somewhat egg-shaped, with very obvious teeth along the entire margin. Leaves are paler on the underside, covered with long spreading hairs and rounded at the apex.

Flowers have a shape described as labiate (applies to all Lamiaceae flowers) with 5 petals varying in their size, fused at their base, produced in leaf axils. One of the identification features for Prostanthera is that the 5 calyx parts (sepals; basal whorl of the flower) are fused into 2 lips.

In this species, 4 to 10 light mauve to bluish flowers appear in leafy clusters at the end of branches with petals to 15 mm long.

Flowering occurs from June to December and makes a pleasant show.

Fruits – 4 tiny nutlets (mericarps) produced at the base of the calyx.

In the garden

An endangered plant in the wild so not commonly grown. However, it can be seen in cultivation in some places such as the Hunter Region Botanic Garden for conservation purposes.

Plants can likely be grown successfully, like many other mint bushes, if they can be sourced.

Not overly large in size and can be easily pruned to keep it smaller and to create density. Tip pruning after flowering is recommended. Plant in part shade and avoid areas that receive hot western sun.

A Prostanthera in full bloom is a magnificent sight and there are so many colours to choose from for your garden. These plants are found in all states in varied soil conditions and climate and thus while it may be a challenge to grow some species many are easy in a garden situation.

A few basic growing tips are:
• Good drainage is essential. Raised beds ensure this
• Water new plants until established, weekly or as required.
• Do not over water, as this can induce root rot and fungal infestation.
• They prefer moist root runs.
• Plant drooping is an indicator of dryness


Plants may be grown from fresh seed. However, cuttings are frequently and reliably used, usually semi-hard wood or soft tip material, which strike well in spring or autumn.

Other information

Prostanthera is a diverse group of about 100 species, endemic to Australia, occurring in all states. There are still many unresolved taxa and species complexes, with new forms regularly being found. Natural hybrids occur between several species and most species appear to be capable of hybridizing when in cultivation. NSW currently has about 52 species, some of which are species-complex and others which are threatened with extinction.

Some 80% of mints contain aromatic oils within their leaves with oil of cineole being a major component. Prostanthera sieberi, P. incisa and P. staurophylla are quite pleasantly overpowering in their exudates when crushed. Positioning of prostantheras as border plants or near pathways is recommended as the mint odour is released when brushed against. Oil from the leaves of some species is distilled for use in cosmetics and as soap additives.

This species likely regenerates from seed after fire, likley after 12 months.

Prostanthera – from the Greek prosthike (προσθήκη) which translates to “addendum” (root of prosthetic), and anthir (ανθήρ) meaning anther – referring to the anthers which have an appendage of tissue.

askania – is named after Askania Park, a private reserve west of Ourimbah, where it grows in sheltered gullies. “Askania” is a name of several localities, as well as a nature reserve, in Russia and the Ukraine, and has Greek roots (Askanios).

Is listed as threatened with extinction with the category of endangered under both Commonwealth and State legislation.

NSW Flora Online (PlantNET) – Prostanthera askania profile page  https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~askania

NSW Office of Environment – Threatened Species Profiles – Prostanthera askania profile page

Wikipedia – Prostanthera askania profile page

Australian Native Plants Society Australia – Prostanthera Information Page

By Jeff Howes. Editing and additional text by Dan Clarke