My rose of Sharon bushes get hundreds of buds but most don't flower - why?
Rose of Sharon
Certified GKH Gardening Expert
There can be a few reasons including environmental, to much or to little water.
Fertilizer issues also can cause this, again to much or to little.
Also Rose Of Sharon can be infected with a fungus call Botrytis and Thrips insects or even a combination of these 2.
A fungicide applied prior to buds forming can help.
Neem Oil is a good treatment since it works as both an insecticide and fungicide. It's safe for people, pets and beneficial bugs.
Here are some links for you.