Q.Why Does My Black-eyed Susan Have No Petals?
They have been beautiful for several years. This year the plants look the same but the flowers have now petals.
Certified GKH Gardening Expert
This could be a case of too much nitrogen and not enough phosphorus and potassium.
Make sure to test your soil for deficiencies and pH swings, which can cause deformed blooms.
I don't see any signs of disease, so it is likely that the nutrient ratios are off.
These articles will help:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/ornamental/flowers/black-eyed-susan/black-eyed-susan-flower.htm