Why timing matters more than technique

Most pruning disasters in British gardens are really calendar disasters. Prune a lilac in March and you will remove the flower buds it formed last summer — you will get plenty of leafy growth and not a single scented bloom. Prune in damp autumn weather and you leave open wounds at exactly the moment fungal spores are drifting around, which is how silverleaf and coral spot find a way in.

The rule that keeps beginners out of trouble is simple. If a shrub flowers before midsummer, prune it straight after flowering. If it flowers after midsummer, prune it in late winter or early spring while it is dormant. Nearly every shrub you are likely to meet fits that pattern, with a few evergreens that need their own approach.

The tools worth owning

You do not need a shed full of equipment, but you do need the right three cutting tools and a way to keep them clean.

• Bypass secateurs — two blades crossing like scissors, for stems up to roughly a finger's thickness.
• Loppers — long handles for branches up to about 4cm across.
• Pruning saw — for anything thicker, because it cuts cleanly where loppers would crush and tear.
• Gloves and a bucket — plus methylated spirits or a weak household disinfectant solution for wiping blades between plants.

Sharpness is not a luxury. A blunt blade crushes plant tissue, and crushed tissue is an open door to disease. Wipe your blades down between shrubs, especially after working on roses, and you will stop problems travelling from one plant to the next.

How to make a cut properly

Cut about 5mm above a bud, or above a pair of buds sitting opposite each other on the stem, at a gentle angle sloping away from the bud. Leave too much and you create a stub that dies back and invites rot. Cut too close and you damage the very bud you want to grow. A steeply slanted cut is best avoided too — it leaves a larger wound that takes longer to seal.

Aim the bud in the direction you want new growth to travel, which for most shrubs means outward, away from the crowded centre of the plant. Make the cut with the thinner blade nearest the part you are keeping, so the blade does not bruise the stem you want to preserve.

For branches too thick for secateurs, use the three-cut method. First make a shallow cut on the underside of the branch about 30cm from the trunk. Then cut from above, slightly further out, so the branch drops away without tearing a strip of bark down the trunk. Finally, cut cleanly back to the swollen collar where the branch meets the trunk, leaving that collar intact.

When to prune: matching the calendar to the shrub

Once you know when a shrub flowers, the timing usually sorts itself out.

• Spring and early-summer flowering shrubs — forsythia, lilac, philadelphus, weigela, deutzia and flowering currant. Prune immediately after flowering, in May or June. Rather than tipping everything lightly, remove two or three of the oldest stems right down at the base.
• Late-summer and autumn flowering shrubs — buddleja, Hydrangea paniculata, hardy fuchsia and caryopteris. Prune in late winter or early spring, and do not be timid. Buddleja cut back to around 60cm from the ground will reward you with bigger, better flowers.
• Evergreens — lavender, hebe and rosemary. Trim lightly after flowering, and finish by late August so the new growth has time to harden before frost. Never cut back into leafless old wood, because most will not regrow from it.
• Dogwoods grown for winter colour — cut back hard in March, just as the buds break, to force the vivid new stems you want the following winter.

Whichever group your shrub belongs to, take no more than a third of the growth in a single year unless you are deliberately renovating an overgrown plant.

Shaping without turning everything into a ball

Shrubs look best when they are allowed to keep their own character, so work with the natural shape rather than against it. Before you start, step back and look at the plant properly. Remove anything dead, diseased or crossing through the centre first, then decide what else genuinely needs to go.

Use thinning cuts — removing a whole stem back to a main branch or the base — to open up the middle of the shrub and let light and air through. Use heading cuts, shortening a stem to a bud, sparingly, because each one triggers a cluster of new shoots. Too many heading cuts give you a dense, twiggy top and a bare, leggy base, which is the opposite of what most shrubs want.

Work in stages rather than in one go. Prune a section, step back, look, then carry on. It is far easier to take a little more off than to put it back.

Common mistakes that catch beginners out

• Shearing everything into tight domes, which strips the shrub of flowers and leaves a brown, twiggy shell.
• Pruning spring-flowering shrubs in winter and losing a whole season of bloom.
• Cutting lavender, rosemary or hebe into old, bare wood in the hope they will bounce back. They rarely do.
• Leaving long stubs above a bud, which die back and let disease in.
• Pruning in autumn, when wounds heal slowly and spores are plentiful.
• Working with blunt or dirty tools, and spreading problems from plant to plant.

Start with one shrub, follow the flowering rule, and keep your blades sharp and clean. After a season or two you will read a plant's growth without thinking about it, and your borders will be the better for it.