Crumbled leaves could be frost damage or lack of water. Too much water would not cause this problem. My guess is that a late frost damaged the tender new growth. Are they shaded from the hot afternoon sun? Sometimes hot sun will scorch new growth. I would just leave the foliage and see what happens. Most likely new growth will appear this summer. There are hardy hydrangeas called Mountain Hydrangeas that can thrive in colder weather without frost damage. If you live where late frost is common you may want to replace your common hydrangeas with a more hardy variety. Keep growing, Marianne Binetti