Both of my hydrangeas have a disease, big black spots on the leaves. They were fine until a week ago. Can you tell me what this is and what I can do to make the hydrangeas healthy once again?
Certified GKH Gardening Expert
It could be either black spot or sooty mold. Both are treatable and, in most cases, not fatal to the plants. These articles will help:
(this is about black spot on roses, but it applies to all plants) https://www.gardeningknowhow.com/ornamental/flowers/roses/black-spot-roses.htm