Late winter (February) or early spring (March), before the leaves begin to appear on the stems, is the best time to prune. This allows the maximum time to enjoy colourful stems, and encourages vigorous new shoots and foliage for the coming season.
Plant roots and shoots are in balance and after hard pruning plants will regrow to re-establish this balance. It is important to prune in the dormant season as the plant resources are largely in the roots and can be used for the required vigorous regrowth. If pruned in summer plant resources are found in the leaves and will be removed upon pruning and regrowth will be less strong.