What sun exposure does your hydrangea receive? For how many hours a day (approx.)? What soil is it in? How is it watered and how often?
I tend a couple of hydrangeas at my MIL's in Palo Alto. I was able to save one, but the other...not.
Since Sacramento is in Sunset Zone 14 and Palo Alto is in Sunset Zone 15, the growing conditions are similar but not alike for hydrangeas as well as other plants, so the particulars of what I did in Palo Alto may help.
Please give me more information about your plant and its health, size, etc., and I'll relate it to what I did as much as I can.
Sunset Zone 17, USDA Zone 9