Answer: Coneflowers (Echinacea) are perennial plants that like full sunshine and ample water during the summertime. If yours were planted in regular soil and were watered routinely, they should have performed well for you. It's natural for the foliage to dieback in the winter time, so perhaps yours were just reacting to a frost. There are not many diseases that attack coneflowers, but the black stems indicate some sort of pathogen was present. Remove all of the plant debris and watch for signs of life from the roots later this summer. Maybe the plants will be okay this year. If things start to look suspicious, dig the plants, roots and all, and destroy them. You can plant some new coneflowers in a different location in the garden.
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