Susie, is the wall of the house there made of brick, by any chance? My mother had a flower bed like that next to a brick wall, wouldn't grow anything well. Turned out it was the mortar between the bricks leaching alkaloids into the soil. (she lived in Vancouver BC, very rainy so lots of leaching) Once she began amending the soil with peat and compost every year, it finally turned around and became more welcoming for plants.
Highly alkaline soil (high pH) actually prevents the absorption of nutrients to a lot of plants.
Also, in my experience Hydrangeas really like a more shady location. I would move the plant before it croaks entirely.
