Pruning marvellous: There's no avoiding it, so you might as well get stuck in. February is the best time to cut back those clematis and buddleia shrubs, says Anna Pavord

If anybody mentions global warming to me again, I'll scream.

After a stretch of the wettest and windiest winter months I can remember for a long time, mud to the horizon, I think we deserved a couple of fine, warm days to remind ourselves why we ever thought we liked gardening. I don't care if we have to pay for it with late frosts in May, the way the doom merchants predict. Last Saturday, I stood among the aconites spreadeagled in the sun, and sniffed like a truffle hound the smell of the viburnum the other side of the path. "Yes!" I thought. "Here we go again." It was such an extraordinary sensation, feeling the sun warm on my back, I could easily have frittered the whole day away. I lifted up snowdrops to look at the odd green punctuation marks on the inner petals. I admired the slaty dark satin colours of the hellebores. I resolved, once again, to divide the blue primroses. But, although I tried hard to maintain the tunnel vision that is so essential in a gardener, it was horribly obvious there was a pressing backlog of work.

Much of it had to do with pruning. February is the time to tackle the later flowering clematis and cut them down to within 18 inches of the ground. They won't die if you don't, but there are good reasons for treating them this way. If you leave them to their own devices, they tend to flower in a bundle high up on the wall or support, leaving you to look into a bird's-nest tangle of bare stems.

If you have planted a late-flowering clematis such as C. viticella to run through an earlier flowering shrub, or accompany a rose, the growth may become so vigorous that the host shrub is suffocated. By clearing out the carapace of clematis each season, you give the supporting shrub breathing space. It can go ahead with its own performance untrammelled, before the clinging clematis smothers it up.

If you have planted clematis to accompany a rose on a pergola, or against a wall, the rose itself will probably need pruning now which, again, means you have to do something about the clematis. The rose/clematis combination is a favourite with gardeners - pink 'Constance Spry' rose with the purple clematis 'Jackmanii Superba', peachy 'Compassion' with the viticella clematis 'Etoile Violette', the generous cluster-flowered rose 'Rambling Rector' with clematis 'Venosa Violacea'. Both partners benefit. They disguise each other's essential gawkiness and the clematis gets a climbing frame to play with. Gardeners get the advantage of two shows on one piece of wall.

'Constance Spry' is usually described as a shrub rose, but it will easily get to 20ft, if it has support. It was bred by David Austin in 1961, so in rose terms it is a new arrival, but it looks old, with big cabbagey double flowers of a not too sickly pink. Austin calls it "myrrh-scented". I always wondered what myrrh smelt like.

If you are faced with a similar combination that needs sorting out, tackle the clematis first (but only if it is the late-flowering kind that responds to February pruning). In a mild winter, it will already have produced plump buds and you feel like a murderer chucking them away, but it has to be done. Cut all the clematis stems down to within 18ins of the ground. Once that is out of the way, you will be able to see more clearly what to do with the rose.

Cut back some of the longest rose growths to about four feet. Pull other stems down, if you can, arching them against the wall as near to horizontal as they will go. This brings the bulk of the rose down towards eye level. It also persuades stems to flower more freely than if they stay upright. 'Constance Spry' has relatively unthorny, pliable stems but some roses are too stiff to treat like this. If you are dealing with a determinedly upright variety, such as 'Compassion', shorten the stems, cutting back if possible to a strong new side shoot and splay the stems out as much as you dare.

If you have C. macropetala or C. alpina rambling through a rose, the whole job will be much trickier. Both of those clematis flower quite early, during April and May. They are already bursting with growth and do not need regular pruning, but it is difficult to prune the rose without cutting back the clematis. Then you lose the best of this season's flowering. You need to bear this in mind when you pair clematis with other climbers. The late types are more suitable companions than the early ones.

Clematis can be roughly divided into three groups: early, mid and late season. The groups dictate whether or not they should be pruned. Early flowering ones need no pruning, mid-season ones can be lightly pruned, late flowering ones need cutting back hard, to within 18 inches of the ground.

But rules are made to be broken. If an early flowering Clematis montana has got rampantly out of hand, as they sometimes do, then I would not hesitate to take the knife to it, tackling it immediately it has finished flowering. Conversely, if I followed the rules, then I would prune our yellow, September-flowering Clematis orientalis every year, but I don't. It does a good job softening a laurel hedge and does not get in the way of any other plants. So it's often left for a couple of years before it is brought to heel. An added advantage of leaving this particular clematis alone is that it then gives you two seasons of bloom. The first is in late May and June, when flowers appear on the growths that have overwintered; the second is in August and September when the clematis flowers on the new growth it has made in the current season.

The young growth of plants often bears bigger, more prolific flowers (and foliage) than the old stuff, which is why buddleia is usually pruned every year about now. No great thunderbolt will fall if you forget to tackle it, but the shrub, a coarse grower at the best of times, will get bigger than it deserves, and the long panicles of bloom will not be as showy as they should.

Buddleia is very difficult to kill, which is comforting to know when you are a new gardener. If it is an established bush, it will already have four or five main stems, all of which need to be cut hard back. There will usually be a bright, precocious bud, already breaking into leaf, to give you a lead. Cut above the bud, trusting it to zoom away as a strong new shoot.

Pruning has the effect of kick-starting plants into new growth and the general rule is to do it immediately a shrub has finished flowering. The ones that need attention now, though, are mostly those that flower in late summer. You don't prune those when they have finished flowering because you don't want to encourage new growth at a time when it is likely to be caught by frost. You leave them to tick over during winter, but prune them as early as you dare towards the beginning of spring. Then they have as much time as possible to build up new flowering stems by summer.

Like buddleia, caryopteris flowers in August and September, so needs pruning soon. It is a compact shrub, rarely as much as four feet high and wide, with greyish-green leaves and blue flowers, particularly good in the variety 'Kew Blue'. Cut the weakest, scraggiest stems out entirely at ground level and prune the other stems back hard, cutting just above a strong shoot. In severe winters, the top growth is often cut back by frost. Your "pruning" will actually be clearing away wood that is already dead.

Hard pruning is what makes spiraeas, such as S. x bumalda and S. japonica, perform most spectacularly in July and August. One of the best is'Anthony Waterer', which has leaves splashed with pink and cream among the flat, crimson flowers. For the biggest flowers, be brutal. Prune all the stems down now to within three or four inches of the ground.

Buddleia, caryopteris, late-flowering clematis, cotinus (for the best display of foliage), dogwood ( Cornus alba), winter-flowering jasmine ( Jasminum nudiflorum), mahonia, photinia 'Red Robin' (if it needs to be reduced in size), rose, snowberry ( Symphoricarpos albus), spiraea, willow (for the best-coloured stems), weigela, wisteria