I made a mistake this year with my white hydrangeas, I cut them almost to ground level. I was reading the instructions and merrily went ahead. It was only when I had finished I discovered that I was reading the wrong label and should not have pruned them at all! I was so annoyed with myself. I did get a few flowers but nothing that matched their splendour last year.
Here is a painting from last year that shows how big these hydrangea flowers get:
Oil on canvas panel
This painting is for sale on Dailypaintworks HERE