Answer: Rose-of-Sharon wilts quite readily in dry soil. If the curling is more pronounced than the wilting, I would suspect aphids. They are greenish, pear-shaped insects that cause curling of the leaves and weakened plants. Look closely at the undersides of the leaves where they tend to congregate. Insecticidal soap is one relatively nontoxic control for aphids.
Another possible cause of the curled leaves is damage from a weed killer applied to nearby lawn areas. If your lawn has been treated with an herbicide, flushing the chemical through the soil with repeated waterings might help.
Of course, there are other possibilities, and since you have so many plants that are affected, it might be worth having a landscaper visit your yard to help diagnose the problem. Good luck.
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