Hydrangea leaves are sick and dying
We have 3 hydrangeas which have white spots, brown and black areas. The plants are 3 years old, 2 on a South-facing slope, but all 3 are in the sun most if not all day. Summer was brutal like usual and we had an usually long, wet Spring.
Certified GKH Gardening Expert
Unless these are Tree Hydrangeas, then full sun will kill them over time. Most other hydrangeas are meant for shade or only partial sun, though some can tolerate close to full sun over time.
If these are a tree hydrangea, then you might chalk this up to a soil infection. A fungicide will be in order here. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
This collection of articles will help you with the care of hydrangeas: https://www.gardeningknowhow.com/category/ornamental/shrubs/hydrangea