All I know about hydrangeas is that they are the ph test strips of the natural world, and they bloom different colors according the acidity of your soil. Our soil is apparently whatever acidity makes blue, because that's what our hydrangea bush blooms.
The only other thing I know about hydrangeas is that they are apparently indestructible. This bush is located right next to where we put the dumpster every year, and it's had plaster thrown into it, boards dropped on it, and all manner of terrible things happening around it, and it still blooms gorgeously every year. I certainly don't water it or pay attention to it, so it's doing this all on its own. Go little hydrangea, go!