Prostanthera cuneata. alpine mint bush

Hmmmm! Minus 30 in winter eh? Well Cestina, that is a continental winter for you.

Plant it in the most sheltered part of your garden. Your summer temperatures are of course fine but you may have to fleece it in the worst weather during winter. Here in the uk (surrounded by water as we are) that at least moderates us so we can grow this here. We have one up in Northumberland in the north east of England that has done fine for quite a few years now.

I would take a few cuttings of it right now to overwinter on a bright windowsill over winter just in case.

Sounds like another one to be in that window in your cool, unheated house, Cestina;-)

Yes, I'm wondering whether to split it up now in fact, or leave it in its pot (or a slightly bigger one) and do as Bamboo suggests, not planting it out till I get back in early May next year.

Good thing I have lots of broad window sills - I think this time round the blinds/curtains will have to be left more or less open.....so far I have mentally assembled hydrangeas, pelargoniums, alpine mint bush (what's it doing with a name like that if it isn't truly frost hardy?) and plumbago. Not to speak of the pot plants in the house. Thank goodness the fuchsias go elsewhere.

It's a woody based shrub so I would take cuttings rather than split it up though Cestina.

These are beautiful plants, they have white small orchid type flowers from the tips of the branches. It is a New Zealand plant so it may stand a chance here. I'd leave it in tact until Spring and plant it in a ceramic pot that can be moved to a warmer position/shed/greenhouse if you think it will suffer. I have 3 in my garden, I am going to leave them insitu and cross my fingers. They will grow up to 3' tall and across