They transpire moisture rapidly, and wilt fast on hot days. Water hydrangeas well during bloom. The blooms often droop on my hydrangeas from heat and water loss. So any plants that are in flower should be kept well watered. A good soaking every four days is much more beneficial than a light watering every day.
Roots can grow shallow in soil that is watered too lightly.
Roots move to the top of the soil for the moisture. They fail to penetrate deeply if the soil is not watered deeply. There is very little difference in them, but Anabelle is supposed to be an improved form. Have the plants shipped in fall, about the middle of October. It is easier to establish the plant in fall than in spring.