There are about 40 Eupatarium species of native North American wildflowers available and they like room to romp and form large clumps. They are all members of the Aster genus and bear clusters of small fuzzy flowers in summer and early fall. Most will self sow and will grow in sun or part shade and prefer moist or wet soils, though they will grow in drier locations.
Joe-Pye Weed is perhaps the best known of the clan and the hollow stemmed Joe Pye Weed with pink flowers grows 5-10 ft while the species with purple spots on its stems, grows between 4-7 feet. One needs a large space to accommodate these plants.
Eupatatium coelestinum is known as the Hardy Ageratum Mistflower, and it resembles the annual ageratum in flower form but is perennial and grows 2-3 ft in zones 5 to 9. It blooms August to September when the cool blue flower heads are especially welcome.
However, we should be careful where we put it as it spreads rapidly by underground rhizomes. Actually we should think carefully before planting any eupatorium plants in small gardens as these natives are best suited to a meadow or dedicated wildflower garden.