Start With the Shrub, Not the Secateurs

Pruning frightens a lot of gardeners, and understandably so. Cut in the wrong place and you can lose a whole season of flowers; cut at the wrong time and you may lose two. The good news is that most shrubs are far more forgiving than we give them credit for, and once you understand why you are cutting, the where and when tend to look after themselves.

Before you reach for the secateurs, ask yourself what you actually want from the plant. Are you removing dead or damaged growth? Keeping it to a sensible size in a small space? Encouraging more flowers? Or opening up the centre so light and air can move through? Each of those aims calls for a slightly different approach, and none of them requires you to hack the whole shrub back to the ground.

Two Questions That Decide the Timing

Almost every shrub in a British garden can be sorted by asking two questions. First: does it flower on wood it grew last year, or on growth it makes this year? Second: when does it flower?

• Flowers before midsummer — it is flowering on last year's wood. Prune straight after the flowers fade, in late spring or early summer, so the plant has time to build next year's flowering stems.
• Flowers after midsummer — it is flowering on this year's new growth. Prune in late winter or early spring, just as growth restarts.

Write the flowering month on a plant label if it helps. A shrub that flowers in May and a shrub that flowers in September need opposite treatment, and treating them the same is the single most common reason for a disappointing display.

Shrubs That Flower Before Midsummer

Forsythia, lilac, mock orange, deutzia, weigela, kerria and flowering currant all fall into this group. They give you their show, then spend the rest of the year quietly making the shoots that will carry next spring's buds. Prune them in June or early July, once the flowers have gone over.

Rather than shearing the top into a tidy dome, work from the base. Take out one in five of the oldest, thickest stems, cutting them low down near ground level. Then shorten any remaining shoots that are spoiling the shape. This keeps the shrub young at the base, where the strongest growth comes from, and stops it developing a dense outer shell with a bare, flowerless middle.

Shrubs That Flower After Midsummer

Buddleja, caryopteris, perovskia, hydrangea paniculata and hardy fuchsias all flower on the current season's growth. Leave them alone through winter — the old stems protect the crown from frost — and cut them back in March or early April as the buds begin to swell.

• Buddleja davidii: cut hard, to within 60–90cm of the ground, to a permanent framework. You will get fewer but much larger flower spikes.
• Hydrangea paniculata: cut back to a low framework of two or three pairs of buds to encourage big, bold cones.
• Mophead and lacecap hydrangeas: treat with more caution. They flower on old wood, so simply remove the faded heads in March and take out any weak or crossing stems. Cutting them hard costs you flowers.

Dead Wood, and Exactly Where to Cut

Whatever the shrub and whenever you prune it, always begin by removing what is dead, damaged or diseased — the "three Ds" — plus any stems rubbing against each other. Dead wood is dull brown and hollow-sounding when tapped; live wood is green or white and firm.

When you shorten a stem, cut back to a healthy bud or a natural fork in the branch. Position the blades about 5mm above an outward-facing bud, angling the cut slightly away from it so water runs off rather than sitting in the bud. Cutting too far above leaves a stub that dies back; cutting too close damages the bud itself.

For anything thicker than your thumb, use a pruning saw and make a small undercut first, then cut from above. This prevents the weight of the branch tearing a strip of bark off the trunk. Never cut flush against the trunk — leave the slight swelling of the branch collar intact, as this is the plant's own healing tissue.

Evergreens, Containers and Tight Spaces

Most conifers and many evergreens will not regrow from old, bare wood, so never cut into leafless stems unless you are happy for the gap to remain. Trim lightly each year, staying within the green growth. Yew, box, holly and bay are the exceptions and will reshoot from old wood quite happily.

In a small garden or on a balcony, the aim is to keep shrubs in proportion rather than to renovate them. Little and often beats one brutal session: a light tidy in spring, a quick trim after flowering, and a check for dead wood in autumn. Use sharp bypass secateurs for stems up to finger thickness and keep the blades clean between plants, particularly if you have been cutting anything diseased.

Finally, be kind to yourself about mistakes. A shrub that has been cut at the wrong moment will usually forgive you within a season or two — and the one you left alone altogether will almost certainly be fine.