Gardening: Shoots to kill

Cutting new growth may seem drastic, writes Anna Pavord, but you've got to be cruel to be kind

If anybody mentions global warming to me again, I'll scream. After a stretch of the wettest and most unpleasant 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. Valentine's weekend was a miracle. I don't care if we have to pay for it with late frosts in May, as 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 on 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 that there was a vast 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 18in of the ground. They won't die if you don't, but 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 to 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. I certainly needed to do some work on the `Constance Spry' rose planted on the south front of the house, which was tangled up with a vigorous Clematis `Jackmanii Superba'.

`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'd always wondered what myrrh smelt like.

The rose was doing wonders for any acrobat who happened to be hanging out of our attic window, but not much for anyone else. Fortunately the clematis was the type that responds to February pruning. I cut all its stems down first, although I felt like a murderer chucking away all the plump buds that were already springing up. Once the clematis was out of the way, I could see more clearly what to do with the rose. Some of the longest growths had to be cut back to about 4ft.

Other stems I pulled down, arching them against the wall as near to horizontal as they would go. This brought the bulk of the rose down towards eye level. It will also persuade the stems to flower more freely than if they were vertical. Some roses are too stiff to treat like this, but `Constance Spry' has relatively unthorny, pliable stems.

If C macropetala or C alpina had been rambling through the `Constance Spry' rose, the whole job would have been 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. It would have been difficult to retrain the rose without cutting back the clematis, but if it had been one of the early ones, we would have lost this season's flowering. You need to bear this in mind when you pair clematis with other climbers.

Clematis can be divided into three groups - early, mid- and late-season - which 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 18in 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 immediately it had 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 of softening a bare stone wall, and does not get in the way of any other plants. So it's often left for five or six years before it is brought to heel. And rejuvenated.

That is another good reason for pruning. Young growths often flower better and with bigger flowers than old ones, 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 be.

Buddleia is difficult to kill, which is comforting to know when you are a new gardener cruising round it wondering where to plunge in the knife. 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 this, 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 them in autumn, because you don't want to encourage new growth that may be caught by frost. You leave them to tick over in winter, but prune them as early as you dare towards the beginning of spring. Then they have time 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 4ft 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 in fact 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', with leaves splashed with pink and cream among the flat, crimson flowers. For the biggest flowers, be brutal. Prune all the stems down to within 3in or 4in of the ground.