I have heard that they are still healthy, but I don't know what I can do to get full petals. . . some have almost none at all.
How Can I Get My Purple Coneflowers to Have Full Petals?
Certified GKH Gardening Expert
It is possible that the coneflowers are being affected by Eriophyid mites, which live and feed on the insides of flower buds. Damage can be recognized by stunted growth and distorted flowers. Treatment of these insect pests can usually be achieved with insecticidal soap sprays or neem oil. I actually like the latter, as it is also an effective fungicide should any other issues pop up as a result of the insects. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Another possibility for the distorted flowers in a disease called Aster yellows, which can actually be transmitted through insects. Here is more information: https://www.gardeningknowhow.com/plant-problems/disease/aster-yellows-disease.htm