Once leaves have fallen deciduous trees and shrubs become dormant and gardeners can start winter pruning. Frosts are not damaging to newly pruned plants in Britain. The tree or shrub has stored its food reserves in the roots, so regrowth will be strong in the spring. Some plants are usually left until February or March – buddleja, most clematis and roses, for example – although winter pruning is not too risky if needs must. In fact, some trimming now is often worthwhile to avoid wind damage before the main pruning later.
Evergreens do not go dormant, ticking over all winter. Pruning evergreens in winter removes leaves needed to keep the roots alive, so garrya and rhododendrons, for example, are best pruned in spring just before growth starts.
Why prune?
Plants shed or “self-prune” shoots and branches in nature due to disease, wind damage or shade. This allows them to allocate their resources to the most productive parts of the tree, which aids their survival by promoting seed production or shading out rival plants. Sometimes “pruning” is forced upon them by browsing animals, wind damage or falling nearby trees. Woody plants have evolved to recover from this natural “pruning”, and they recover from pruning by gardeners, too.
Dead, diseased, crossing or rubbing shoots are removed to maintain plant health.
Pruning to reduce plant size is important in gardens. Because winter-pruned deciduous trees and shrubs rebound vigorously, many gardeners doubt winter pruning actually results in a small plant, but in fact it does.
Pruning can promote flowering and fruiting. Ornamental shrubs are pruned according to when they flower; late winter for those flowering in late summer to maximise time for new flowering shoots to grow. Spring and summer flowering shrubs are pruned after flowering to maximise time for new shoots to form to flower the following year. Soft fruit is usually pruned in winter.
Wisteria form whippy shoots following summer pruning, which are shortened in winter to three or four buds so the flowers are easier to enjoy.
Winter, when the branches and shape are most easily seen, allows trees to be pruned into graceful forms with the desired length of trunk and position of branches. Step back from time to time to assess progress in case you inadvertently cut out more than intended.
For shrubs, shaping typically involves thinning congested growth and removing wayward shoots. Some trim into a round “blob”, but labour-saving seldom allows shrubs to display their best.
Winter pruning is a powerful tool and wise gardeners use it with restraint and err on the side of caution, because once removed shoots cannot be replaced and several years of regrowth might pass before they can be pruned again.
Renovation
Renovation – in effect starting again – is when overgrown trees, shrubs and climbers are severely pruned to induce regrowth.
With deciduous plants, with their food reserves safe underground, winter is the ideal time to renovate, such as when trees and shrubs have grown very large and annual pruning has proved insufficient to keep them within their allotted space.
Beech and hornbeam hedges, for example, tend to spread each year, getting wider and taller until there is no choice but to prune drastically. Cutting back one side and the top to where the hedge should be will induce strong summer growth that can be trimmed to reshape the hedge. The remaining side is dealt with in future years once the cut top and side recover.
Similarly, outsize shrubs and climbers can be renovated. Most shrubs and climbers are simply cut to near ground level. They will regrow, but will be smaller and flowering might not resume for a year or two. In the case of lilacs, flowering is delayed for several years. Some delicate shrubs, Japanese maples and witch hazel for example, are best treated to more measured pruning, removing branches over several winters to avoid coarse regrowth and maintain their graceful shape.
Soft fruit
Blackcurrants fruit on new shoots. Cut out one stem in three, choosing the biggest and oldest shoots, to the base to encourage strong new shoots each year. Gooseberries and currants fruit on older wood and, here, the new growth is shortened one or two buds in winter to keep the plant compact and fruitful. Prune out older shoots to a strong replacement sideshoot if this is needed on mature, larger bushes. Congested growth can be thinned to ease harvesting. Grapevines are pruned after leaf fall to avoid sap “bleeding” in spring. Here, side shoots are cut back to the main stems or rods. The sideshoots regrow strongly in spring and flower.
Fruit trees
Apples and pear trees are winter-pruned to remove some the older, less fruitful wood and promote replacement shoots. Typically 10-20 per cent of branches are removed each winter, spread evenly around the tree. Most of the remaining branches should be about four years old – you can age a branch by looking for the annual joint between each year’s growth.
Overgrown fruit trees are often ill-advisedly shorn, resulting in thick vigorous unfruitful growth. Restore these trees over several years by removing congested branches so the remaining ones are about 50-60cm apart at the base. Remove weeping branches and cut back tall, vigorous ones to a more horizontal sideshoot. If more than 25 per cent of the canopy is removed in one winter the tree becomes unbalanced, resulting in unproductive regrowth.
Plums, cherries, including ornamental ones, are vulnerable if pruned in the winter, because disease spores can infect through the open wounds. They need little pruning, but if necessary prune these in spring or early summer.
Trees
Mature ornamental trees seldom need routine pruning. However, they can be pruned in winter when their shape is not obscured by foliage if too big, or to improve shape, or to remove damaged branches. Where necessary, qualified arborists can prune taller trees safely.
While trees are young, however, winter pruning can help them to develop an attractive shape and avoid weak, acute V-shaped branch junctions liable to split as the tree ages. Remove lower shoots to give the desired length of clean stem and then shape the canopy by removing wayward branches.
Top 5 pruning tools
1. Pruning saw: With a curved blade this is the best winter pruning tool. It enables neat and precise cutting in one direction.
2. Secateurs: Only suitable for thin shoots, gooseberries for example. In winter, most pruning involves thicker timber. Secateurs need frequent sharpening with a diamond sharpener.
3. Loppers: These deal with thicker shoots, but pruning saws usually do a better job. With telescopic handles, loppers can reach higher branches and can avoid bending when cutting up prunings on the ground.
4. Cordless chainsaw: Much more civilised than petrol ones, this tool must be treated with respect. Garden chainsaws cannot tackle thick wood and their charge only lasts for 20 minutes or so, but they can save much labour. Ones mounted on extension poles can be invaluable in avoiding potentially hazardous ladder work.
5. Long-handled pruner: These are loppers on a long stick worked by a lever at the bottom and acting on a rod to work the blades. They are slow but very useful when only a modest amount of pruning at height is needed.
