Mulch might help. We planted a bunch of new ones years ago, and the leaves were wilting in warm weather - in shade - even with daily watering.
Put mulch down, and the leaves perked the next day with new growth in a week.
If you have mulch already, is it all the leaves, or older inner leaves?
Could be associated with root weevil damage too. In that case, you may see some damage just below the mulch or soil line. If that's the case - its a goner.