Many gardeners have questions about pruning. The main concern is what plants to prune and when to prune them. The major factor in deciding when to prune is whether or when the plant flowers or sets blooms.
Light, corrective pruning can be done any time of the year and will reduce the need for severe pruning, which might weaken the plant. When severe pruning becomes necessary it should be done in late winter or early spring. Pruning in late summer should be limited because new growth might not have time to mature before cold weather.