Hydrangea petiolaris is an Asian species of climbing hydrangea. These types of hydrangeas should not be pruned when they are young.
The ideal time to prune the mature hydrangea petiolaris is immediately after it finishes flowering. This gives the plant time to recover from the pruning session before it is ready to produce new buds.
Prune as little as possible from the hydrangea petiolaris. The more you cut, the fewer flowers it will produce so cut judiciously. Remove dead canes by cutting back to healthy wood or a main cane. Trim the stems to keep them to the support structure or the shape you desire.
Before going into the garden, dip the pruning shears into a solution of 1 part household disinfectant and 5 parts of water. Allow them to sit in the solution for two minutes, and rinse them with clean water.