When and how to prune the Pinky Winky hydrangea?
This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/prune-hydrangea-bushes-hydrangea-pruning-instructions.htm
I have a hydrangea "Pinky Winky." Can it be pruned to form a tree? If so, how?
Pinky Winky can be trained as a small single trunk tree. During late winter/early spring, you could try removing 1/3 of the plant’s lateral small branches from the ground up. Then, cut away any crossed branches or those that aren’t growing away from the middle of the plant. Here is an article that has some more guidelines:
http://blog.pennlive.com/gardening/2012/10/can_i_make_a_pinky_winky_hydra.html
Happy gardening!