Answer: Most hydrangeas will look droopy in the midday sunshine so what you describe is normal. The plants recover overnight and look fine the following morning. You can avoid this by replanting your hydrangeas in a site that is protected from hot afternoon sunshine. The bigleaf hydrangeas (H. macrophylla) such as Nikko blue bloom on stems that grew last year, so you do not want to remove those stems if you can help it. You can remove the spent flowers plus a few inches of stem, but don't prune off too much. Winterkill or dieback does sometimes kill those stems back to ground level, but you need to be very patient about trimming them off, just to make sure. This dieback is most common if the plant is located in a windy spot or in an exposed spot; fertilizing in late summer or fall can also contribute to it, as can a dry fall season.
Wait until early spring when the plants begin to leaf out to do any pruning. Since yours will flower on new shoots that develop from old wood, don't prune your shrubs back too drastically or you'll lose all the blooms for the season.
Nikko blue hydrangeas will be their bluest in acid soil. You could use a granular slow release fertilizer for acid loving plants such as Hollytone according to the label instructions. You might also want to check the pH of your soil to make sure it is in an acceptable range for you hydrangea (a pH of 5.0 to 5.5 is sufficiently acid to produce blue, while 6.0 to 6.5 will encourage a pink coloring). Good luck with your hydrangeas.
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