Brown leaves on hydrangeas are not uncommon. Sometimes care errors, the weather or the location are to blame.
Hydrangeas usually prefer partially shaded locations. If they are exposed to too much direct sunlight, their leaves can burn in spots and develop brown or yellow spots. A lack of certain nutrients such as nitrogen or potassium can lead to brown to yellow or reddish leaves, and sometimes the plant also stops growing. Too much fertilizer can also cause discolored leaves. The affected or diseased leaves should definitely be removed and disposed of in the trash. The leaves or buds turn brown and even mushy in spring? This may be an indication that at least parts of the plant have frozen. In most cases it can still be saved, but most of the flowers will probably fail this season. You only cut off frozen branches in mid-May so as not to further weaken the plant. If there is a risk of cold snaps and as a precaution against frost next autumn, cover the root area with a layer of mulch.