Hydrangea red leaves
My huge old hydrangea has developed some red leaves. Some of them die off at the edges. Some leaves have dropped off. It is a very vigorous plant, prolific in flowers. I have been recommended to use what is in affect epsom salts to help with a magnesium deficiency. Some of the flowers, just coming out are blue-ish, presumably due to the epsom salts. It has never shown any blue before. Is this the correct treatment for this condition? I read somewhere that it might be caused by a phosphorous deficiency. Will the epsom salts help with this (If its true) or do I need something else?