Coneflower Petals Soft And Black

Question

Every year, sometimes just a few flowers on one plant, sometimes entire plant.

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Answer 1

The area, likely, receives too much water! Being a drought resistant flower, I would opt for a drier area for planting. Otherwise, a fungicide may be able to help mitigate some of the damage done by the contaminants.

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

https://www.gardeningknowhow.com/ornamental/flowers/coneflower