Pruning shrubs correctly for healthy growth

Why pruning matters more than you think

Pruning is one of those jobs that divides gardeners. Some of us sharpen the secateurs with real enthusiasm, snipping at anything that looks untidy. Others hover nervously, convinced that one wrong cut will finish off a beloved shrub for good. The truth sits somewhere in the middle, and it is much more forgiving than most people fear.

A well-pruned shrub is not simply a tidier shrub. Regular cutting lets light and air reach the centre of the plant, which reduces the risk of fungal problems such as powdery mildew and grey mould. It encourages fresh, vigorous growth and, on flowering shrubs, it often means more blooms rather than fewer. It also gives you the chance to steer the plant's shape while it is still young, rather than wrestling with an overgrown monster in ten years' time.

The golden rule is simple: remove dead wood first, then shape the plant lightly once it has finished flowering. Everything else is detail.

Start with the three Ds

Before you think about shape at all, work through what gardeners call the three Ds: dead, damaged and diseased. This is the clearing work, and it should always come first because everything you do afterwards depends on it.

• Dead wood is dry, brittle and usually a dull grey-brown. Snap a thin stem in your fingers; if it cracks cleanly with no green tissue inside, it is dead. Cut it back to healthy growth or to the base.
• Damaged wood includes branches snapped by wind, rubbed raw by a fence, or sliced by a strimmer. These wounds are open doors for infection, so tidy them back to sound timber with a clean cut.
• Diseased wood may show blackened patches, sunken cankers, orange spores or powdery coatings. Cut well below the affected area, into clean wood, and wipe your blades with a diluted disinfectant between cuts so you do not carry the problem to the next stem.

Once the three Ds are gone, you will often find the plant already looks better and you have hardly touched its shape. Resist the urge to keep going just because the secateurs are out.

Timing: the one rule worth remembering

If you learn nothing else, learn this. Prune spring and early summer flowering shrubs straight after they flower. That covers favourites such as forsythia, lilac, ribes, weigela and philadelphus. These plants build their flower buds on growth made the previous year, so if you cut them in winter or early spring you are simply removing this season's display before it happens.

Shrubs that flower on the current season's growth, including buddleja, caryopteris, hydrangea paniculata and most potentillas, are pruned in late winter or early spring, just as buds begin to swell. Cutting them back hard in March encourages strong new shoots that will carry flowers by summer.

Evergreens are a little different again. Most respond best to light trimming in late spring or early summer, once the risk of hard frost has passed. Never cut into old, bare wood on a conifer, because most will not regrow from it, and you will be left with a permanent brown patch.

How to make a clean cut

Good technique protects the plant and helps it heal quickly. Always cut just above a bud, a sideshoot or a strong outward-facing branch, and angle the cut away from the bud so water runs off rather than sitting on it.

• Use bypass secateurs for living stems up to about the thickness of your thumb. Anvil types crush rather than slice and are best kept for dead wood.
• For anything thicker than a pencil, use loppers, and for branches over 3cm reach for a pruning saw. Forcing a cut with the wrong tool leaves a ragged wound.
• Cut back to a branch collar — the slight swelling where a branch meets the trunk — rather than leaving a long stub. Stubs die back and invite disease.
• Keep blades sharp and clean. A sharp cut slices cleanly; a blunt one bruises. Wipe blades with methylated spirits between plants if you suspect disease.
• Take no more than a quarter to a third of the plant's growth in a single year, unless you are deliberately renovating an old, neglected shrub over two or three seasons.

Shaping without going too far

Once the structural work is done, shaping is a light touch. Step back frequently and look at the whole plant rather than the branch in front of you. Aim for an open, goblet-like framework where light can reach the middle, and remove any stems that cross and rub, or that crowd the centre.

If you are creating a hedge or a formal shape, trim little and often through the growing season rather than one drastic cut. Little and often keeps the surface dense and green, and it is far less stressful for the plant. For most flowering shrubs, a gentle tidy that removes the oldest stems at the base every couple of years is enough to keep them youthful and blooming well.

Finish by clearing away all prunings, especially any diseased material, and give the shrub a mulch of garden compost and a watering in dry spells. A plant that has just been cut is putting energy into new growth, and a little kindness afterwards pays you back generously. Pruning is not an act of aggression; done thoughtfully, it is one of the kindest things you can do for a shrub.