Securing a patch of tranquility
Published On
23/12/2025Tranquillity Mintbush (Prostanthera askania) is a rare plant that is unique to the Central Coast. It has a very restricted geographic range, occurring in only 11 small populations mostly within a 20km radius around Niagara Park, Ourimbah, Fountaindale, Glenning Valley and Holgate/Matcham. The species is listed as Endangered under both NSW and Commonwealth legislation due to its restricted range, small population sizes, limited number of plants protected in conservation areas and threats including habitat loss, degradation from weed invasion, trampling and inappropriate fire regimes. A Recovery Plan was finalised for the species in 2006.
P. askania is a beautifully fragrant shrub growing from 1-3 metres high with a spreading, sometimes scrambling habit. The leaves are ovate with a deeply toothed margin and are much larger (12-25mm in length) than the more common Prostanthera incisa and Prostanthera incana that often co-occur with P. askania. Its branches and leaves are densely covered with long hairs which is another key identifying feature of the species. It flowers in Spring, putting on a wonderful show of blue-mauve.
The species most often occurs in the upper reaches of creeks on the lower valley slopes, although some individuals also occur on upper slopes and ridges. It occurs in both warm temperate rainforest and moist sclerophyll forests, and the ecotone between them. It is thought to be a colonising species, taking advantage of increased light following natural canopy-cover disturbance.
The NSW Saving our Species (SoS) program has a conservation strategy for P. askania that identifies five priority management sites and conservation actions to manage the critical threats. Weed control is a key conservation action across all sites, although further actions are required to secure the species.
At one priority management site in a Council natural area, SoS have recorded a dramatic decline in the size of the population of P. askania over the past 20 years. It is thought that this is a result of increasing shading of the mintbush by the midstorey layer of the vegetation. Recent genetic testing of the remaining 20 individuals at the site has revealed that this population has unique genetic variation not observed in the other known populations. It is therefore important to preserve the genetic diversity of this population and implement actions to promote and increase the population size.
In spring 2025, Council’s skilled nursery team and SoS staff worked together to carefully collect cutting material from the site. The initial aim is to grow and maintain stock plants for each individual from the site. It is then planned to propagate more stock that can be planted back at the site in May/June 2026, further upslope where there is less shading. This action is intended to supplement the existing population, boosting the number of individuals, whilst still maintaining the genetic diversity of plants at the site. Our Environmental Volunteer Program Nursery Volunteers will be involved in the production of these very important plants in the nursery until they are ready to be planted back at the site. They will also be involved with ongoing maintenance of the valuable stock plants that will be held at the nursery for future propagation and planting activities.
Another action that is being trialled at the site is thinning of the mid storey plants around the P. askania. The initial results have been positive, with an increase in P. askania size and health in response to these management actions!
Propagation to supplement population size is also being conducted at another priority management site for P. askania in Strickland State Forest. At this site, stock produced by the Hunter Region Botanic Gardens was planted out in Autumn 2025 and is showing strong survival rates. Extensive weed control was undertaken prior to the planting and continues to be managed by Friends of Strickland volunteers and Forestry Corporation of NSW. The work at both sites is helping to improve our understanding of the species and how best to conserve it.
Image: Prostanthera askania branches with flowers, if only a photo could capture the aroma!
Collecting cutting material
Propagation time back at the nursery.
Up to 20 cuttings were produced per individual P. askania.
This article was written by Sharyn Styman, Conservation Management Officer