Ninebark, known botanically as Physocarpus, is a genus of flowering and fruiting perennial shrubs in the rose family of plants. Like most woody deciduous shrubs, they require no mandatory pruning for performance but do benefit from the removal of damage and dead wood. They can also be pruned to maintain their proper footprint in the surrounding landscape design should they become overgrown.
Prune your ninebark shrubs in the early spring while the shrub is still dormant and before new growth and buds have emerged.
Cut back any dead or diseased branches or any plant tissues that look compromised or suspect. Cut back to a point of healthy plant tissue and pull the questionable cuttings from the shrub and discard them. If an entire branch is compromised, cut it off at the crown of the plant just above the soil line.
Reduce the size and spread of the shrub by cutting off the terminal branch tips to the desired length. Never reduce the shrub by more than one-third of its size in any single pruning session, in order to prevent shock. Place all cuts on the bias just a 1/4 inch above a leaf node or bud. Work evenly around the shrub following the natural form to ensure an attractive and natural-looking result.
Rejuvenate a hollowed out shrub or defoliated stems by conducting renewal pruning every few years or as needed. Remove one-third of the oldest and barest branches down to the crown of the plant just above the soil level. This will spur new shoots to fill out the interior and lower perimeter of the plant.