dropping leaves on hydrangea
my little spit fire hydrangea leaves suddenly dropping The soil is moist
Certified GKH Gardening Expert
Avoid watering from above and directly into the center of the plant.
This can cause root rot.
Allow the soil to dry slightly between waterings. Pull back any mulch at least 6 inches from the base of the plant.
Remove and discard any leaves that have dropped, this can help stop the spread of fungus or leaf diseases.
Look for any markings on the leaves.
This link will describe the most common diseases and the symptoms to look for.