Too many purple coneflowers
I have a wildflower garden on my septic mound but the purple coneflowers are taking over. What can I do to control them, and grow other wildflowers. They get over 5' tall and bloom like crazy. The light is east and south. I live north of Northfield
Dakota County Minnesota
Hello and thank you for contacting AaE for help.Gardening on a septic mound should be approached with caution. It is advised not to disturb the soil too much. That said, I would recommend carefully pulling up some of the Purple coneflowers and add such plants as Milkweed (Asclepias tuberosa) which would provide a nice color contrast. Then surround the taller plants with Daylilies (Hemerocalis spp.), Liatris and mounding Prairie Dropseed (Sporobolus heterolepsis). These plants should hold their own even if coneflowers do crop up among them.
There are more suggested plants like these that hold the soil and do well in a dryer environment like a septic mound listed in the PDF link here which comes from the U of MN Extension service book entitled, "The Best Plants for 30 Tough Sites."
I hope this helps.