Answer: It sounds like the flowers are getting too wet before they open. Overhead watering or rain can cause this. Or, the flower buds may be host to little bud worms. These pests feed on the petals of the unopened flowers. The flowers won't open when this happens. There's not much you can do to discourge the bud worms other than pick the affected flowers off the plant so you can control the next generation. Best wishes with your petunias.
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