Prostanthera incana is a medium shrub that reaches a height of 2.5 metres with a 2-metre spread.
It has a distribution mainly in NSW; growing along the coast and coastal inland, with most records between Eden and Newcastle with some disjunction. It grows in the Blue Mountains and north-west of Dungog. There are some records just south of the Queensland border around Urbenville; and there are some scattered records through north-eastern Victoria (near Dargo).
It is typically found in tall dry sclerophyll forest as well as woodland, often on skeletal sandy soils overlying sandstone.
Prostanthera have simple, opposite and usually odorous leaves (a typical Lamiaceae feature). In this species, leaves are two centimetres long, oval, dull-green-grey, aromatic with a velvety appearance (hence the common name). Leaf margins have rounded teeth.
Flowers have a shape described as labiate (applied to all Lamiaceae flowers) with petals varying in their size, purple to lilac, 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, flowers are one centimetre long, lilac, pink or sometimes white and carried in clusters. Blooms are conspicuous, copious and appear in late spring and summer. Both foliage and flowers are attractive features.
Fruits are mericarps (can be called nutlets). Four are produced produced at the base of the calyx.
This species is known to be cultivated and is reported to be hardy. It grows well on sandy soils with good drainage in dappled light.
After flowering a light prune is appreciated.
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
Positioning of prostantheras as border plants or near pathways is recommended as the mint odour is released when brushed against.
As with all mintbushes, this species propagates readily from cuttings.
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.
The type specimen was collected in the Warragamba area, NSW in the early 1800s.
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. Oil from the leaves of some species is distilled for use in cosmetics and as soap additives.
Likely regenerates from seed after fire, possibly 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.
incana – Latin meaning “grey” or “hoary” – referring to the hairy appearance of the foliage.
This species is not considered to be at risk of extinction in the wild.
NSW Flora Online (PlantNET) – Prostanthera incana profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~incana
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.
Plantmark Wholsale Nurseries – Prostanthera incana sales page https://www.plantmark.com.au/prostanthera-incana