Pruning is not about containing a shrub or tree. Its purpose is to enable the plant to become more beautiful and contribute more to the garden than if left to its own devices.
Pruning is done to promote bigger harvests, get newly-planted trees and shrubs off to a good start, thin crowded stems, train cordons, fans and espaliers, encourage flowering, shape plants, remove diseased wood and promote vigour. With a few exceptions, all of these jobs can be done in winter, when bare stems make the job of shaping shrubs and spotting diseased growth much easier.
For details on how to prune, see our practical project How to winter-prune trees and shrubs.
In this feature, we explain why and what to prune in winter.