Can't tell for sure but it's possible you're overwatering -- you say you water often -- how dry is the soil when you water? Both echinacea and coreposis are not going to like wet feet. The soil may have stayed damp too long and caused root rot, which will cause the plant to wilt (because the roots can't take up water any more). The plants will often turn mushy and black and pull up easily. Additional water at that point won't help. It might be good to take a look at the soil, determine the type of soil and how well-drained it is, and see how dry it gets between your normal waterings. Weekly deep soakings are better for your plants than more frequent ones.

There may be other problems at work but that seems the most likely suspect. They're both tough, vigorous plants that do well even with some degree of neglect so disease problems aren't as likely.

My first guess is that if you cut back on the water you might solve your problem, but others may have other insights.

Good luck!

carol ann, you are absolutely correct. I have been over watering my plants like crazy! I spoke to a master gardener today and she told me the very same thing. I did test the soil and it is so moist. I kept thinking watering it every other day would be good but I was doing most of the plants more damage than good. I do have good drainage but with the heavy mulching that I do and the heavy twice a day water it was too much for the Echinacea, Coreopsis and the Shasta Daisies. I still plan on doing a test of the soil to be a 101% assured but for now, all fingers point to over watering. Thank you for the response.

You're welcome -- glad you figured out the problem, and good luck with your flowers! I'm betting now that you have the watering figured out, your flowers will flourish. Enjoy, and happy gardening!