Salvia guaranitica gone wild in dry shade under trees
Salvia guaranitica is one of the hardiest Salvias even if you live in a climate where the winters go down to below -12C. It is a rampant grower with a suckering habit. You could plant it in a difficult site, such as the one pictured here and be delighted by the continual display of rich blue flowers over summer and autumn. My suggestion is to try some of the cultivars which may be more well behaved than the straight species. These include 'Argentina Skies', 'Black and Blue', 'Costa Rica Blue' and 'Violet Eyes'
2017 update: I currently have stock of 'Black and Blue'