Prostanthera hirtula

Hairy Mintbush

Family: Lamiaceae

A spreading shrub to 2 metres tall by 1 metre wide.

It is found on elevated, rocky sites in dry sclerophyll woodland and open forest in New South Wales. It has some disjunct records, but is generally found from the southern Blue Mountains to the Budawang Range and further on the south coast into southern Victoria. There are also some isolated records in central NSW and on the North Coast.

Branches densely covered with more or less spreading hairs. The whole plant is strongly aromatic. Stems square to somewhat rounded.

Leaves in opposite pairs (rarely in 3-leaf whorls), strongly aromatic, to 3 cm long and only 0.6 cm wide, creating a linear to narrow-elliptic shape, mid-green coloured and moderately to densely hairy.

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 (basal whorl of the flower) are fused into 2 lips.

In this species, flowers are dark mauve, to 10 mm long, with petals fused to form a bell-shaped tube. Flowers are produced in the leaf axils, in raceme-like groups or clusters, often leafy at the base. Flowering occurs in spring.

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

In the garden

Not overly common in cultivation and hard to source online.

It could likely be grown on a well-drained soil in full sun to part shade.

Tip prune after flowering to create a denser habit and more flowering the following season.

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

Propagation

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

There are approximately 100 species, endemic to Australia. They occur in all states.

This genus is currently under revision, and several species complexes are unresolved. Natural hybrids occur between several species and most species appear to be capable of hybridising when in cultivation.

Some 80% of mints contain aromatic oils within their leaves with oil of cineol being a major component. Prostanthera sieberi, P. incisa and P. staurophylla are quite pleasantly overpowering due to 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.

Most Prostanthera will regenerate from seed after fire with some species exhibiting an ability to reshoot from basal areas and stem buds. The exact response for this species is unknown.

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

hirtula – Latin – generally meaning “hairy”.

 

https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Prostanthera
http://anpsa.org.au/APOL2007/apr07-1.html

https://en.wikipedia.org/wiki/Prostanthera_hirtula
https://apps.lucidcentral.org/plants_se_nsw/text/entities/prostanthera_hirtula.htm

By Jeff Howes, edited by Dan Clarke