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 on how to winter-prune trees and shrubs.
In this feature, we explain why and what to prune in winter.
Fruit trees or bushes left to their own devices divide energy between fruit production and making new growth. Having established a framework, the object of pruning is to persuade the plants to maximise fruiting, cutting each lateral branch back to two or three buds from the main branch. This differs with various types of fruiting plant. For example, with apples, you prune to promote fruiting spurs, with pears you open up the trees to ripen the wood and with blackcurrants you remove old wood.
When shrubs or trees are newly planted it's vital to encourage formation of a good root system, so it's worth sacrificing over-active new growth by cutting it back to a few buds. New shrubs should be cut back to reduce demands on roots in the first season, new fruit bushes should be thinned to just three branches, and new trees should be pruned to reduce the 'sail' effect of top growth, to prevent wind rock.
Some plants whose growth is constantly renewed from ground level should have their weak, spindly shoots removed, as well as a quantity of the oldest stems. With plants such as dogwood, Cornus stolonifera, the stems that have lost their bright colour should be removed. With plants such as hazel, Corylus avellana, the oldest shoots should be thinned out to prevent overcrowding. Simply remove large branches from older shrubs.
Training fruit trees
Having established the main framework by tying in major branches to the support, side shoots should be reduced to two or three buds to make short spurs. Much of the work should be done in August and September, but it can be continued into winter. Apples should be pruned as cordons or espaliers, pears should be trained as espaliers or fans and apricots and peaches should be trained as fans.
Promoting summer blooms
Any shrub that flowers after midsummer can produce flowers on new growth, so these shrubs can be manipulated to ensure the flowers grow at the desired height. Branches can either be cut back hard or thinned into a nice shape. Large shrubs such as buddleia should be pruned hard to stop growth getting out of control, while smaller shrubs such as hardy fuchsias should be cut back to promote larger blooms.
Winter is the ideal time to assess and modify the shape and structure of trees and shrubs. It's difficult to evaluate what's happening when they're covered in leaves. With crab apples, lop-sided shoots should be removed, while competing leading shoots should be taken out of trees such as rowan. Shrubs such as Viburnum opulus should be pruned into a vase shape.
Diseased branches should be pruned out to maintain the health of trees and shrubs, however winter pruning of plums and related species during winter should be avoided, as this can lead to the spread of silver-leaf disease. Apples and pears should be pruned to remove branches infected with canker, magnolias should have dead stems removed to control verticillium wilt, and other trees and shrubs should be pruned to remove die-back and crossing branches.
Pruning in this way removes weaker stems to promote stronger growth of existing stems, or removes existing stems altogether to encourage fresh, new growth. Plants grown for their colourful winter stems, such as dogwood, Cornus alba, and white willow, Salix alba, should be cut back hard or 'stooled' in late winter or early spring, to around 15cm above ground level. Other shrubs should have the thinnest, spindly growth removed.