A dwarf macrophylla hydrangea, Pia grows only 2-1/2 feet tall and wide. Pia also stays pink in soil conditions that would turn most hydrangeas blue. To keep your Pia hydrangea compact and healthy, prune it annually in the late summer once blooms have past. Pruning at other times of year results in fewer blossoms.
Check for damaged or dead branches. Low lying branches may get trampled and bruised by critters. Older stems can die; these will have yellowed leaves and dull woody stems.
Prepare a 1:10 solution of bleach:water in a small bucket. Dip your pruning shears in this solution, then clip off a dead or damaged branch at its intersection with the trunk. Dip your pruners in the solution again, then make the next cut. Remove all damaged and dead growth in this manner. Clean your pruners again and dry them with a towel before continuing.
Cut off weak shoots that develop near the base of the plant, eliminating both old and new weak growth.
Remove any stems that do not bear flowers.
Head back the hydrangea to keep it smaller and more compact. Trim back all branches by several inches, keeping a uniform shape all around.