What is wrong with my hydrangeas?
My hydrangeas all have the same problem. The leaves turn brown and shrivel up at the edges.They finally fall off. The plants do not grow. I have sprayed for bugs and also with neem oil. They are all in partial shade and get plenty of water every few days.
Monterey County California
There are several diseases of hydrangeas. Botrytis blight is one that seems to match your symptoms most closely. Though this is typically a greenhouse disease, high humidity and leaf wetness can cause it to occur in the landscape. Control of this disease is to control the environment. Keep plants healthy by avoiding any stresses such as plants staying too wet or too dry, chemical or mechanical injury, and too little or too much fertilizer. Improve air circulation and sunlight. Avoid over head watering. Especially keep open flowers with many petals dry. There are some fungicides to help prevent or reduce leaf, fruit and stem infections. Sanitation may be helpful, but is not perfect since the disease can blow in from a long distance. Dead head dying flowers and remove all infected plant tissue.
There is a publication at the following link that talks about several common diseases of hydrangea.