Gardening: The short cuts to a colourful summer: As the new season's growth stirs, Anna Pavord suggests a pruning programme to bring the best out of your shrubs

We are almost at the end of the 'slowest' period of the year. Things are on the move, with brilliant crocuses lolling on their backs in the intermittent sunshine, and snowdrops flowering fit to bust.

Despite the shock, the hellebores are still in full flow in an unprepossessing border under the yews on the east side of the house. Unfortunately, the slatey-grey flowered ones introduced last year are only pushing up leaves. Extra rations there this year. The Cyclamen coum are going flat out; so are the primroses. Some wise gardener once said that the secret of successful gardening was to find out what likes you and then grow a lot of it. On this damp, heavy soil, primroses grow leaves like banana palms, and flower well, too.

If you have ordinary primroses in the garden alongside named varieties, you will find all kinds of muddy crosses appearing. They are opportunistic breeders. 'Sue Jervis' is a double, a pale, peachy pink that looks good with the clear blue of a pulmonaria or with a variegated brunnera. 'Corporal Baxter' is a deep-red double, luscious and robust. 'Miss Indigo' is a startling double blue, with a fine silvery lacing round the edges of the petals. Those I can vouch for; for the rest, see Mary Robinson's Primulas: The Complete Guide (Crowood, pounds 15.95).

Do not waste double primroses on dry, thin ground. Dig in plenty of compost or, even better, manure, wherever they are to grow. Like other classic cottage-garden plants, they need chamberpot culture. Grow them where they will be shaded in summer, but not where they will dry out. The plants clump up meatily where they are happy. To keep them flowering well, you should split them every other year.

The simplest way is to ease out the clump and pull it apart with your hands. It is quite easy to see where the breaks should come, for the plant arranges itself in a series of crowns, each of which will make a new plant. Add bonemeal when replanting, and do not let the plants dry out.

That job is in the future. There are plenty that need doing now that do not involve touching the soil, which is still as squelchy as an overfilled meat pie. First, head for the wistaria, a plant loaded with dreams, fantasies of bowers and house fronts, pergolas and arches dripping with long tassels of elegant blooms. But you have to make those dreams come true: prune severely to jolt the plant into making flower buds rather than more growth buds.

Pruning is usually done in two stages, half in summer, when you shorten the shoots you do not want, and half now, when you cut them back to within two buds of the previous year's growth. You need to be up the ladder while reading this, so it becomes much more obvious how to tackle the job. The whole task is made immeasurably easier if the main growths of wistaria are trained on wires. Then you can see clearly the growths needed to extend the framework and the ones that can be lopped off. When you are training, bear in mind that the Japanese wistaria winds clockwise, the Chinese anti-clockwise. If in doubt, follow the direction the tendrils seem to be taking for themselves. I find it difficult to transfer the concept of 'clockwise' into different planes, and sway at the top of the ladder, rolling my head round and round like a hypnotised snake.

After the wistaria, buddleia. Buddleia is a tough bully of a shrub, so do not feel sorry for it when you chop down branches that are, this winter, already in full leaf. If you do not prune, the thing becomes unbearable, and the flower quality suffers.

Take down the wands of last year's new growth to within two buds of the old wood. Cut out thin and wispy stems entirely. When you have finished, the stump will look horrific. It should, if you have done the job properly; but buddleia grows so fast the damage will soon be camouflaged.

While you are still feeling savage, turn to dogwoods. Actually, you can allow your aggression to peter out quietly on this shrub if you want. The standard manuals tell you to cut growths of all dogwoods grown for their decorative winter bark right down to the ground each year. I cut only half, in rotation, which puts the poor things under less stress. If you grow the variegated dogwood, Cornus alba 'Elegantissima', and leave half the stems in situ, you will reap the benefit of the variegated foliage earlier in the season.

Jasmine needs more thought in pruning than any of the previous shrubs, though it all too seldom receives it. A brutal redesign is often its fate, transforming it from a languid, weeping, waterfalling sort of shrub into a bristling hedgehog. Prune it by keeping as many as possible of the long, bright-green shoots that will flower next season, and cutting out bristly growths. If there are one or two good strong green stems arising from the base of the plant, cut out the same number of old stems entirely, at the base, to encourage more of this kind of regeneration.

Pin the old buff growths as high up the wall or support as you can, and allow the green growths that spring from them to fall in a kind of bead curtain in front of them. Do not clip the bush all over.

Tackle mahonia, too, if you want the tassels of flowers to remain within sniffing distance. A young bush will not need attention - it is only when you realise that you are looking at stems rather than leaves that steps need be taken. Each year shorten the longest stem by at least half, cutting above a side shoot or the old leaf scars from which a bud might shoot if pushed hard enough.

Most hydrangeas need thinning, rather than drastic pruning. The old flowerheads that have been left over winter to provide cover against frost can be whipped off now. Cut back to where a strong pair of leaves or buds are ready to take over. Cut out the spindliest stems entirely to encourage good new growth from the base.

You need to be tougher with Hydrangea paniculata, where size of flower is all that matters. The blooms of 'Grandiflora' can be up to 18in long, appearing in August and September. When they first come out they are white, but then flush gently to pink.

Prune this hydrangea like the buddleia, taking all the previous season's growth back to within two buds of the old wood. The purpose is the same in both cases: to force the shrub to produce the vigorous growth that will carry the best flowers.

A lot of pruning is fuelled by fear. The shrub's owner feels that it is getting out of hand. Reducing the shrub's size is the only aim. Take the trouble to understand the consequences of your pruning. Ponder its effect on the shrub you are attacking. The results will be a hundred times better.