A variable shrub that may reach a height of 5 metres by about 4 metres wide.
It has a large natural range, growing along the coast and inland of NSW, as far south as the very south-east corner of the State, extending to Mallacoota in Victoria (with further records to the west as far as the Geelong-area); extending to as far west as Griffith in NSW, east to Cowra, with a lot of records in the Sydney area (north of the harbour mainly), as well as Wisemans Ferry; extending in disjunct occurrences up the coast and inland, to as far north as Rockhampton-area is Queensland.
This cultivar is sold as Prostanthera ovalifolia ‘Rosea’. It has not been determined what is different about this cultivar (very little information is available online). The name suggests it may have flowers which are more mauve-pink.
Prostanthera have simple, opposite and usually odorous leaves. In this cultivar, the leaves are ovate to narrow-ovate, to 50 mm long by 10 mm wide (widest in the middle), mid to dark green with the lower surface paler and densely coverd with glands.
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 cultivar, flowers are to 1 cm long, bright mauve to purple or bluish-purple; arranged in terminal clusters or botryoids, occurring profusely in spring.
Fruits are mericarps (can be called nutlets). Four are produced produced at the base of the calyx.
Prostanthera ovalifolia ‘Rosea’. is the one I grow and prefer. It has lovely mauve flowers that cover the plant for a far too short a period in Spring. It was the first mint bush that I grew in my garden in the northern Sydney suburb of Westleigh and the original plant lasted for well over 20 years.
It is stunning in flower and has the added bonus of highly aromatic leaves – when brushed they fill the air with a delightful bushland fragrance. It is a rounded shrub that grows to about two to three metres tall with a similar spread.
My plants are growing in a thin layer of topsoil over a clay sub soil in a well drained position and they do receive some additional watering in dry spells. They are very hardy and grow best in a position with part shade (they will tolerate a sunny position) and well drained soil.
Prostanthera ovalifolia ‘Rosea’ is often considered to be short lived by many gardeners. I have not found this to be the case and one of the reasons may be that I do not keep the plant growing continually by providing ample moisture, especially in autumn/winter. They need a resting period, as in nature, when dry periods allow the plant to harden new growth and have a rest from growing. So keep the water up to the plant in summer and do not worry too much if there are the occasional dry spells for up to a month.
The only maintenance required is to give them a good hard pruning after each flowering to keep it from becoming ‘leggy’ and to promote better flowering next season. I remove about a third of last season’s growth. They can be pruned even harder if needed. While I do not give them any fertiliser after planting, they do respond well to annual fertilising after flowering.
I recommend that you grow three or more different together plants because when in flower the subtle differences in colours between different species create a lovely effect. The main flowers colours are white, pink, mauves and blues. The rarer Prostantheras have yellow and even red flowers.
Must be propagated from cuttings to retain the cultivar traits.
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.
ovalifolia – Latin – referring to the roughly oval-shaped leaves of the species.
‘Rosea’ – exact meaning unknown but refers to ‘Rose’ – which may refer to the colour of the flowers or their appearance.
NSW Flora Online (PlantNET) – Prostanthera ovalifolia profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~ovalifolia
Gardening with Angus – Prostanthera ovalifolia profile page https://www.gardeningwithangus.com.au/prostanthera-ovalifolia-oval-leaved-mint-bush/
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.