My cosmos flowers were growing well and then started to shrivel up and distort prior to dying off. Why is this happening?
Distortion of flowers can be due to insects or disease.
Inspect the plant to see if you see any issues.
Treat the plants with Neem Oil. Neem Oil works as both an insecticide and fungicide.
It is also safe for people, pets and bees.
Here are some links with more information.