Gardening: Beautiful but badly behaved

If I were starting again (dread words) I would plant only late- flowering clematis on a pergola, or indeed anywhere that the clematis was likely to mix itself up with a rose that needed pruning. On paper, the idea of having early, mid-season and late-flowering clematis on the pergola seemed sound. It would extend the flowering season - something that gardening correspondents are always going on about, even to themselves.

As I tenderly planted April-flowering Clematis macropetala to surge through the rose `Easlea's Golden Rambler', and as I swathed the incumbent solanum with fresh tendrils of the May-flowering clematis `The President', I did not realise what complications I was making for myself. Both clematis have gone mad. But the solanum has now died and is impossible to extricate from its suit of borrowed clothes, and I can't fight my way through the enveloping blankets of C macropetala to prune the rose when I need to.

If I had planted just late-flowering types of C viticella, all the clematis could have been cut down close to the ground in February and the way would be clear for me to get in and do whatever work was necessary on the host shrubs.

But I didn't. So the solanum will have to stay until some disaster hits the clematis too, when I can get both out of the way and start afresh. It's difficult, though, to limit yourself - even in one part of the garden - to one season of flowering, given a family such as the clematis which can provide flowers in almost any month of the year.

The season starts with creamy-yellow, freckled C cirrhosa, often in bloom by February. It's not such a thug as C armandii, which flowers through March and April. Both those are evergreen, unlike the glorious spring- flowering kinds derived from C macropetala and C alpina. Flowers get bigger as the season advances, so you end up in midsummer with dinner plates such as mid-blue `General Sikorski' and dark red `Niobe'.

By August and September, when the viticellas are at their best, the flower size has shrunk. In many situations, this is an advantage. Scent is heaviest in the autumn-flowering kinds such as white C flammula, and C rehderiana which smells of cowslips.

The time of flowering to a great extent governs how you should prune your clematis. An enormous fuss is made about this subject. Some gardeners thoroughly enjoy fussing, so rather than deprive them of hours of profitable worry, I recommend a week with a good book (see box).

In terms of pruning, clematis fall into three categories: those that need none, those that need a light touch, and those that respond to butchering. The "none" option, of course, is the easiest, and it is worth remembering that a clematis will not die from lack of pruning. It may flower less than it otherwise would. It may flower at gutter rather than at eye level. But it will not keel over just because you and your flashing Felcos have not been near it.

You need never prune the earliest flowering clematis, such as delicate C alpina types (`Francis Rivis' and his friends), vigorous C armandii, C macropetala and the popular C montana, though both this and C armandii may need cutting back if they are bullying other plants. If you want to reduce their spread, prune them immediately after flowering. Otherwise leave them alone. I don't prune the yellow, autumn-flowering C tangutica, either, though some people treat it as a group three (hard prune) type. Ours mounds itself over a wall, flowering magnificently with no attention, so it gets none.

If clematis do need pruning, then do it in February. Subjects for light pruning include the popular `Nelly Moser' (mauve with a lilac bar), `Barbara Jackman', `Lasurstern' and `The President', all of which are out at the moment. Light pruning means taking out dead, weak, or scraggy-looking stems, entirely and cutting the rest of the stems back to the first strong pair of buds you can find. These will already be showing themselves plainly by the end of February.

The clematis that need the toughest treatment are those that flower in the second half of summer: the beautiful purple `Jackmanii Superba', mauve- pink `Comtesse de Bouchaud', sky-blue `Perle d'Azur' and the Viticellas (my favourites), such as the reddish `Abundance' and deep purple `Royal Velours'.

All these should be cut back hard to within a foot or so of the ground. This is cathartic and gives you an opportunity each year to train properly and tie in the fresh stems to avoid an unholy tangle of growth. At the same time you can mulch all your clematis with compost or manure to keep the soil moist and the roots cool. More important than pruning, though, is the position in which you plant your clematis. By nature, clematis are scramblers; they have no means by which they can stick themselves to supports. They are, however, beautifully equipped for hoisting themselves through some other growing things, and this is how they look best.

A clematis plant is not in itself a thing of beauty. It has no particular form. Its flowers are its only raison d'etre.

As it has naturally evolved as a scrambler, clematis thrives best with its feet in the shade and its head in the sun. Grown through some host such as ceanothus or viburnum, these conditions occur without much effort on your part. `Mrs Cholmondeley' threading its way through an April-flowering ceanothus will keep decently out of the limelight until the ceanothus has finished its display and then quietly take over a starring role in late May and June. Or you could use the greenish-white C florida `Alba Plena' with a summer-flowering ceanothus.

Half a dozen little interferences in spring is all it takes to persuade a clematis to range experimentally over a wide area rather than bunch its stems altogether in a single, matted twist. `Jackmanii Superba', a particularly vigorous variety with sumptuous velvety blooms of deep purple, responds particularly well to this gentle nudging. I have it on a south wall of the house where it wanders among the wisteria. A bush of rue, a peony and other neighbours prevent the sun from shining too hotly on the clematis roots. A thick mulch of muck in late spring also provides insulation - and food, for if the clematis is sharing space with a host shrub, it is also sharing food and drink. Make sure there is plenty of both.

`Jackmanii Superba' is quite happy with this south aspect. `Nelly Moser' would not be. The flowers, pale mauve with vivid carmine bars running from base to tip of each petal, fade badly in full sunshine. The same is true of the similar `Marcel Moser' and `Bees Jubilee'.

These are best on east or west walls, but will also flower on north-facing walls, provided that they are not hideously exposed. The elegant white `Marie Boisselot' is happy with a sunless north aspect. So is the pale blue `Lady Northcliffe'. Pale clematis shine out in dark corners. Dark purple here would be glum.

Clematis Address Book

READ CLEMATIS by Christopher Lloyd (Viking); The Gardener's Guide to Growing Clematis by Raymond Evison (David & Charles)

SEE CLEMATIS at: Great Dixter, Northiam, East Sussex TN31 6PH, open daily (not Mon) 2pm-5pm, admission pounds 3; 115 Hadlow Road, Tonbridge, Kent, open 12 July, 2pm-6pm, admission pounds 1.50; 133 Crystal Palace Road, London SE22, open 5 July, 2pm-6pm, admission pounds 1; The Mews Cottage, Harrogate, open 29 July, 2pm-5.30pm, admission pounds 1.50.

JOIN THE International Clematis Society, 3 Cuthberts Close, Cheshunt, Waltham Cross EN7 5RB (01992 636524); British Clematis Society, 4 Springfield, Lightwater, Surrey GU18 5XP (01276 476387). National Collections Treasures of Tenbury, Burford House Gardens, Tenbury Wells, Worcs WR15 8HQ (01584 810777); The Guernsey Clematis Nursery, Domarie Vineries, Les Sauvagees, St Sampson, Guernsey CI (01481 45942).

BUY FROM Great Dixter Nurseries, as above (01797 253107); Pennells, Newark Road, South Hykeham, Lincoln LN6 9NT (01522 880044); Thorncroft, The Lings, Reymerston, Norwich, Norfolk NR9 4QG (01953 850407).