Buds Fail to Open on Rose of Sharon

I have a pink rose of Sharon bush that is 4 years old. It buds fully, but then the blooms fail to open. What is the problem? My white rose of Sharon opens just fine.

Some plants, like people, are more susceptible to stress. Too much or not enough water or fertilizer can cause buds to drop before opening. Start by evaluating the current growing conditions. Though both plants receive the same care the soil or light may vary causing problems for the pink flowering variety and not your white one. For best results keep the soil moist, avoiding extremes on either end. Mulch the surrounding soil with shredded leaves, bark or other material to help keep conserve water and keep the soil consistently moist. Avoid excess fertilization. Most gardeners tend to kill their plants with kindness than neglect. Have a soil test to find out what changes, if any you need to make with your feeding schedule. 

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