Many factors cause dropping buds, but most of them concern your plant’s environment. While the Rose of Sharon can handle hot weather, constant exposure to temperatures over 90 degrees Fahrenheit can be harmful. In addition to prolonged heat, dropping buds are also caused by excessively low humidity.
If these conditions are not the problem, continue troubleshooting by checking your water and fertilizer. Dropping buds may be an indicator of overfeeding, so lessen your use of fertilizer. Also, check its watering conditions. Too much or too little water can also be the culprit.