Rose of Sharon
My Rose of Sharon shrub has an abundance of buds on each branch, but only a very small amount actually bloom. The shrub is in a well drained spot and gets about 10 hours of sun each day. Why won't all buds bloom??
Too little water or too much fertilizer are two of the most common causes of "bud drop" or bud rot on the Rose of Sharon. Depending on the zone you're in, this year's temperatures have been particularly high, so try increasing the water (make sure the soil well-drained) and add a light covering of organic mulch.
This article may help you: