Great Blue Lobelia, Lobelia siphilitica
This clump-forming cousin to the cardinal flower--sometimes also called blue cardinal flower--blooms from late summer to mid-autumn in blue to lavender-blue spikes. Prefers moist soil; plant in wetter areas and fertilize early in the growing season to encourage heavier blooming. This delicate-looking flower has a long bloom time and is very hardy except in hot, dry weather. Keep moist and consider planting in part sun to protect this blue beauty.