Answer: Hydrangeas can suffer transplant stress, a symptom of which could be drying leaves due to moisture stress. A late frost could also cause some foliage damage, as could excess wind if transported in an open vehicle or even excessive fertilization. Make sure the soil is kept evenly moist but not sopping wet while the plants are becoming established; this is also the degree of moisture these plants prefer in general. This will help them recover and grow new foliage. Trim away any dead leaves.
The spots could be caused by a fungal or bacterial infection but based on your description I am unable to make a specific diagnosis. In general, remove any badly disfigured leaves, avoid wetting the foliage, and planting in an area with good air circulation would help limit the spread. I would also suggest you consult with the nursery where you purchased the plants (since they are new plants) and/or your county extension for a definite diagnosis and suggestions as to what steps to take next.
Good luck with your hydrangeas!
Q&A Library Searching Tips