Prostanthera, Round Leaf Mint Bush, Australian Mint Bush 'Ghost Cave'

This plant is one of the lovliest shrubs I have ever grown in the ground in Vancouver. I have grown this plant on more than one occ...Read Moreasion.

I live in a climate where we experience, usually, what is considered by the USDA to be zone 7b. We frequently experience zone 8a winters. I grew this plant outside in Vancouver, British Columbia for two winters in a sheltered area between mine and the neighbours one-storey houses in an area that recieves about six hours of direct sun a day in the summer. The third winter we had our coldest winter in 40 years (zone 7a or -15 Celcius/5 Fahrenheit) where it did freeze and die. In this city we get about 1600 mm or 62 inches of rain a year. When considering hardiness we always have to consider that cold hardiness ratings don't confirm that plants will survive the winter. There are many plants from arid regions that can tolerate much more cold than Vancouver can provide, but from my experience will rot very quickly and die as soon as the winter rains begin. Prostanthera rotundifolia has proven to be tolerant of both the cold (most of the time) and the constant wet conditions. At least in my postal code area, V5V 1K6.

It appears to be very drought tolerant in the summer too. This spring I planted one on Salt Spring Island in a spot where the temperature reaches up to 37 Celsius/100 Fahrenheit at ground level. It was only watered maybe 10 times during the whole summer. It didn't grow alot, but it is still green and didn't lose any leaves that I could see.

When I have grown it in Vacouver it grows very rapidly into a 1 metre/3 ft lush shrub that is almost obscured by it's little purple flowers when it blooms and the scent is 'delicious' and bubblegum-like. I think even though it is not completely hardy it is worth growing in climates like this and comparably Seattle. It's sold as an annual here but could effectively be treated as a short lived perennial notwithstanding that the unpredictability of the weather could potentially kill it during it's first winter. It is deciduous here, not evergreen. It's generally not a very expensive plant. A small cutting in a four inch pot can grow in our climate in good soil to at least 24 in the first season.

I live in Zone 8, but love the plant so much I buy it anyway and treat it as an annual. It has a lovely fragrance and form. Maybe I can...Read More protect it this winter.