Clematis pruning groups 1, 2 and 3 explained

Ask a room of gardeners what worries them about clematis and pruning will come up within a minute. The good news is that the whole subject rests on one question: when does your plant flower, and on what wood? Answer that and the three pruning groups fall into place.

Why clematis are split into groups

Some clematis carry their flowers on stems that grew the previous year; others flower on shoots produced in the current season. Cut the first kind hard in winter and you remove this year's flower buds. Leave the second kind unpruned and it simply carries on from where it stopped last autumn, flowering higher and higher above a bare tangle of old stems. The three groups used by the RHS and the British Clematis Society are shorthand for these two habits, with a middle group that does a bit of both.

The British Clematis Society sums it up in a single rule of thumb: if it flowers before June, don't prune it in winter. The RHS gives the same advice for plants whose group you don't know: those flowering before June shouldn't be pruned, while those flowering from late June onwards can be pruned in February.

Group 1: early flowerers

Group 1 covers clematis that flower from winter to the end of May on growth made the previous year. It includes C. alpina, C. macropetala, C. montana, the evergreen C. armandii and C. cirrhosa, and the New Zealand hybrids.

What to do

• Little or no routine pruning is needed. Removing faded flowers and a light tidy is enough for most plants.
• If a plant has outgrown its space, prune it straight after flowering, once the risk of frost has passed, so that it has the rest of the growing season to make next year's flowering wood.
• For winter-flowering types such as C. cirrhosa, the British Clematis Society advises leaving the new green stems alone, because they carry the winter flowers. Tidy brown growth only once fresh green growth is visible.

Renovating a neglected group 1 plant is possible. The RHS suggests cutting stems to about 15cm from the base after flowering, but not repeating this within three years, because it affects flowering. A big montana can take a while to recover, so only renovate when you really have to.

Group 2: early large-flowered hybrids

Group 2 contains the large-flowered hybrids that open their first and biggest flush from late May to June on short shoots from last year's stems, often followed by a smaller second flush in late summer. Familiar examples on the RHS list include 'Nelly Moser', 'Bees' Jubilee', 'Doctor Ruppel', 'Marie Boisselot', 'The President' and 'Snow Queen'.

The late-winter tidy

In February or early March, remove dead, weak and broken stems. Then, working down from the top of each remaining stem, cut just above the first pair of plump, healthy buds you find. This is a light trim, not a haircut: the RHS warns that heavy pruning at this stage costs you flowers, and the British Clematis Society points out that cutting lower removes the wood that carries the early blooms.

After the first flush

Once the early flowers fade, you can cut some stems back to a large bud or strong side shoot just below the spent blooms to encourage a second flush. If the plant has become top-heavy, the RHS suggests reducing it gradually over two or three seasons by pruning harder after the first flush. Alternatively, every three or four years you can cut the whole plant back to 30–90cm in late winter, group 3 style, accepting a single, later flush that year.

Group 3: late-summer flowerers

Group 3 clematis flower from late June onwards on stems produced that same year. They include viticellas such as 'Étoile Violette' and 'Polish Spirit', the texensis hybrid 'Princess Diana', 'Ernest Markham', 'Ville de Lyon' and the non-clinging 'Alionushka'. Their simple pruning is one reason they are the usual choice for growing through roses.

How hard to cut

These are the easiest clematis to prune. In February or March, cut every stem back to the lowest pair of healthy buds, which the RHS puts at roughly 15–30cm above soil level. The British Clematis Society phrases it as cutting just above the second pair of live buds, counting up from the base, and removing everything above. In colder, northern gardens this can wait until April. Don't rush: very early hard pruning can expose tender new shoots to frost.

The Society also suggests pinching out the tips when new growth reaches about 30cm, just above the top leaf joint. This doubles the number of stems and so increases flowering.

The exception: seedhead clematis

Small-flowered types grown partly for their seedheads, such as C. tangutica and 'Bill MacKenzie', can instead be thinned and trimmed back to a framework, so you keep the silky seedheads through autumn.

The in-between plants

Some popular summer clematis sit happily in either group 2 or group 3. The RHS names 'Comtesse de Bouchaud', 'Gipsy Queen', 'Hagley Hybrid', 'Jackmanii', 'Perle d'Azur', 'Rouge Cardinal' and 'Star of India'. A useful approach is to keep a basic framework on some stems and cut others hard to the base. This staggers flowering and lengthens the season.

Pruning a newly planted clematis

Whatever the group, young plants benefit from a hard cut early on to encourage several stems from the base. For groups 2 and 3, the RHS advises that, unless the plant already has three or four healthy stems, you cut it back in the first spring after planting to just above a strong pair of buds about 30cm from the soil. Our guide to planting a clematis covers this step in more detail.

If you have lost the label

• Watch the plant for a season and note when it flowers.
• Flowers before June: treat it as group 1 and leave it alone in winter.
• Large flowers in May and June, and perhaps again later: treat it as group 2.
• Flowers from late June onwards: treat it as group 3.

A wrong guess is rarely fatal; at worst you lose a season's flowers. If a clematis refuses to bloom even when you prune it correctly, look at its growing conditions and its feeding and watering before blaming the secateurs.

Tools and technique

• Use clean, sharp secateurs and cut just above a pair of buds.
• Untangle carefully: clematis stems are brittle, and a stem that looks dead at the top is often alive lower down.
• Tie in new growth with soft twine in loose figure-of-eight loops as it extends, spacing stems evenly across the support.