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About two years ago I was searching for free outdoor plants. The owner of one house ended up offering me some datura seedlings and one plant that I have struggled to identify ever since - until today that is! After a few twitter retweets, Mary Butterfield, of the VanDusen Botanical Garden (Vancouver) suggested a plant with very similar flowers. The leaves were too different to be in the same genus so I looked up the broader family 'Lamiaceae' which put me on track to finally identifying it.
The common name of Salvia sclarea var. turkestanica is Vatican Clary Sage. Individual plants grow up to 3ft and in some cases 4ft tall with a spread of about 2ft. They tend to end up in large clumps, dropping new seeds every year which vigorously grow the next spring. They don't generally bloom the first year from seed and die to the ground with freezing temperatures.
They grow best in full sun, have average water needs, and seem resistant to all pests. I haven't seen a single munched on leaf! Between the seeds and pest resistance it can be a little invasive even in a zone 5 garden (allegedly hardy to zone 4). I would recommend growing it either in a pot or surround by stones so it's a bit easier to handle.
The mature flowers will be vertical with the bracts spread much farther apart. The young blooms really are lovely, almost spilling over from the foliage in a white waterfall with light pink edges (many plants are more purple). I hope you enjoy this plant as much as I do!