The weeks after flowering are the sweet spot

The most useful pruning advice I can give any gardener is this: do the job in the fortnight after the flowers fade, not in the depths of winter when you finally have a free Saturday. Shrubs such as forsythia, deutzia, weigela, philadelphus and flowering currant all build next year's flowering buds on the stems they make this summer. Cut them in February and you cut away the very flowers you were hoping for. Cut them in late May or June, while the spent blooms are still visible, and the plant has the whole growing season to build a fresh, tidy framework before autumn.

You can usually tell these shrubs at a glance. They are the ones that were smothered in colour in April, May or early June and have looked like plain green bushes ever since.

Check which shrub you actually have

Before you pick up the secateurs, spend thirty seconds working out when your shrub flowers. It changes everything.

• Spring and early summer flowerers — forsythia, mock orange, weigela, deutzia, kerria, flowering currant, spring ceanothus and broom: prune straight after flowering.
• Late summer and autumn flowerers — buddleja, hydrangea paniculata, caryopteris and abelia: leave them alone for now and cut back in early spring instead.
• Evergreens grown for foliage — choisya, photinia, bay and hebe: a light trim in late spring or midsummer is plenty, and heavy cutting into old, bare wood rarely regrows.
• Lavender and rosemary: trim the flowered stems by a few centimetres only, and never cut back into the leafless old wood lower down.

If you are unsure, wait. A shrub left unpruned for one season will simply look a little shaggy. A shrub pruned at the wrong moment can lose an entire year of flower.

Three jobs, in this order

Once you know the timing is right, work through the bush methodically rather than snipping at random. I do the same three jobs every time.

• Dead, damaged and crossing wood first. This is the easy part. Cut out anything brittle, blackened, split or rubbing against a neighbour. You will often remove a good quarter of the tangle before you have made a single aesthetic decision.
• Take out one or two of the oldest stems at the base. If you can see thick, grey, woody stems with little fresh growth, saw one or two of them off as low as you can reach. Aim to remove no more than one in five stems each year — this renewal pruning keeps the whole shrub young and stops it going bald at the bottom.
• Cut the spent flowering stems back to a strong shoot. Follow each faded stem down to a healthy side shoot or a pair of fat buds, and cut just above it. As a rule of thumb you will be taking off around a third of the length. This is what triggers fresh growth that will carry next year's buds.
• Shape lightly, and stop. Thin out the thickest, most crowded sideshoots so light and air reach the centre, then step back and tidy any lopsided growth. Aim for a bush that is slightly wider at the base than the top, with an open middle.

Making a good cut

Sharp bypass secateurs make clean cuts; blunt ones crush the stem and leave a wound that invites disease. Cut about 5mm above a bud, on a slight angle sloping away from it, so rainwater runs off rather than sitting in the bud. Wherever possible, cut to a bud that faces outwards — that is the direction the new shoot will grow, and it keeps the centre of the bush open.

Try not to leave long stubs of dead stem, as these die back and look untidy. For anything thicker than your thumb, switch to a pruning saw rather than forcing the secateurs and bruising the bark. Wipe your blades with a cloth and a little methylated spirit between shrubs, particularly if you have been cutting anything diseased, and sharpen them at the end of the session.

Small spaces, pots and balconies

Everything above works just as well on a balcony or in a courtyard, only on a smaller scale. Choose compact or dwarf forms — dwarf weigela, patio buddleja, smaller deutzias, choisya 'Aztec Pearl' — and the same after-flowering routine keeps them from outgrowing their space.

In a container, growth is slower and the plant has less energy to spare, so cut less generously: a light trim of the spent flowering stems is usually enough, with just one old stem removed at the base each year. Keeping a shrub to a neat, manageable size from the start is far easier than trying to reduce an overgrown one later. After pruning, scrape off the top centimetre of compost, top it up with fresh, and water well. A liquid feed every fortnight through the growing season keeps container shrubs flowering their best, and repotting every two or three years stops the rootball turning into a solid brick.

Aftercare, and what to leave alone

Pruning is a shock, even when it is good for the plant. Water it in dry spells, mulch around the base with garden compost or well-rotted manure, and give a balanced feed if the leaves look pale. Avoid heavy nitrogen feeds late in the season, which push out soft growth that winter will damage.

Do not be tempted to tidy autumn flowerers now — mark them with a label and come back in March. And before you put the clippings on the heap, look at the healthiest stems you have removed: cut just below a leaf joint and pushed into gritty compost, many will root into new plants by late summer. Pruning, done at the right moment, is not a chore. It is the simplest way to keep a small garden full of flowers, year after year.