Douglas Justice contributes today’s photo. He writes:
For years, we considered this evergreen mint relative to be–like so many Australian shrubs–only marginally hardy in the Vancouver area. Various sources list its cold hardiness as USDA Zone 9. Nevertheless, this specimen is located in a fairly exposed position in the Australasian section of the E.H. Lohbrunner Alpine Garden and has been growing there since 2001. It has seen both mild (i.e., exceptionally wet) and severe winters, with and without snow cover. The species is both highly aromatic and long flowering.
The Australian National Botanic Gardens has a very good webpage describing Prostanthera cuneata. As well as being somewhat tender, the ANBG write-up mentions that Prostanthera cuneata is “…susceptible to root pathogens, such as Phytophthora cinnamomi and may be short lived in cultivation. This may be alleviated through the purchase of tougher clones, which are now available.” Unfortunately the provenance of the Garden’s thriving plants is unknown. The accession came to us from an anonymous garden visitor.