Pruning Potentillas, Summer Blooming Spireas and Annabelle Hydrangeas
These and other summer flowering shrubs can be pruned back anytime during the dormant season. Consider waiting until late winter or early spring when the plants will recover more quickly.
Cut the whole plant back halfway in late winter. Use a hand pruner and make cuts above a healthy bud. Though it takes longer than a hedge clipper, you will make more precise cuts that will close more quickly, reducing the risk of insects and disease.
Next, take half of these stems, the older and thicker ones, right back to the ground. A lopper will extend your reach into the center of the plant and allow you to cut larger stems if needed.
This will encourage new growth at the base of the plant. Plus, the older stems will provide support for the new growth, reducing floppy appearance.
A bit more information: Increase bloom time on summer blooming spirea. Lightly shear the first set of flowers as they fade. You will be rewarded with a second set of blooms. And if your season is long enough, remove the second set of faded blooms for a third bloom.