Answer: It sounds as though you're doing everything right for your new hydrangeas - rich, moist soil, protection from hot afternoon sunshine, regular water - so the only insight I can offer is 1) newly transplanted shrubs can take several months to become established; until the roots are firmly established, the plants can be stressed by the slightest things that wouldn't bother established plants, and 2) hydrangeas tend to wilt when the weather gets hot - they don't need water, they just need cooler temperatures and that's why they revive overnight and then wilt again the next afternoon. This is a natural process - the plants are trying to cope with hot weather by conserving moisture in the roots and stems rather than sending it to the foliage. Because your plants are new to your garden, they haven't yet developed extensive root systems. Once they have been in place for a season, they should be able to cope with your summer weather. If your other hydrangeas are behaving normally and the reds are not, they're just not mature enough to cope with the environmental conditions in your garden. There is hope for them, though. This summer water them just as often as you water your other hydrangeas - no more, no less. Don't let the afternoon wilting convince you to water more often because you may be over-watering and that would lead to root rot. If the plants perk up by morning, then they're getting enough water. Best wishes with your landscape!
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