Hi, does anyone have experience with growing Gray-headed Coneflower, Ratibida pinnata? It seems to be taking over in a garden where I volunteer. Some of the plants with flowers are almost 6 feet tall. The garden is normally not watered, except for new plantings. I have seen and admired Gray-headed Coneflower growing in the wild, but none were as tall as these. And the crown of each plant must be between 12-14 inches wide, also much wider than what I have experienced in the wild.