Salvia nemorosa
Meadow Sage
This is a very reliable herbaceous perennial. It will take full or half sun, is drought-tolerant, and has a dark purple blue flower spike. It blooms from early summer to autumn if flowers are deadheaded. after two years mine is about 18″ tall and wide but I expect it to get a little bigger before it needs dividing. All salvias bring in the butterflies and this one is no exception in Stillwater. Next year I will try to learn just who is showing up. USDA Zones 4 to 9