hydrangeas

I've got three hydrangeas in my front bed. one of them grows like crazy. the other two get black spots on the leaves and then the black spots spread and then eventually the whole leaf shrivels up. they keep pumping out new leaves, but the same thing keeps happening over and over so it cant grow.

i give all three the same general treatment regarding watering, etc. and they are all three exposed to the same general amount of sunlight / shade.

any ideas?