The parents of this lovely Lacecap variety were found growing on the wooded slope of a Korean mountain, which explains its exceptional hardiness and its preference for shade. It produces delicate clusters of light blue flowers that last for several weeks in early to midsummer (July here in Connecticut), turning a stunning deep crimson as they age. Fall foliage is an attractive shade of burgundy. Excellent in a shady border with Ferns and Astilbes such as "Visions'. 'Blue Billow' is a reliable bloomer through Zone 6, and adventurous gardeners in Zone 5, where flowering occurs three or four years out of five, may also wish to give it a try.