Description: Late summer flowering, North American perennial; deep blue, mist-like flowers in late summer and autumn; attractive burgundy stems
Size: Plants grow to 3 feet high and 4-5 feet wide; spreads by underground runners
Cultural Information: Prefers full sun to light shade and moist, rich loam; pinch back in early summer for a bushier plant
USDA Zones: 3 through 9
Historical Notes: This handsome North American member of the aster family occurs naturally in low moist ground and savannahs, on moist wooded slopes, and along streams from New Jersey to Minnesota and in the West Indies. The species was listed in a British botanical magazine in 1730 and appeared in Philadelphia nurseryman John Bartram's broadside catalogue in 1793. Also known as Hardy Ageratum, this species resembles the cultivated annual Ageratum houstonianum, from Mexico. In 1851, New England garden writer Joseph Breck called it "the most beautiful" Eupatorium.1 Its late-season blooms attract bees and swallowtail butterflies.