Clematis are some of our best-loved flowering climbers but although they are generally easy to grow given the right conditions, there is often confusion about how best to prune them. Some flower well if pruned lightly, while others thrive when cut back hard. The trick is to identify which type you have.
Clematis species and cultivars are divided into three main pruning groups; the plant label should tell you what type you have. A broad rule of thumb, as with many deciduous flowering shrubs and climbers, is that early-flowering (spring and early summer) types require just a light tidy-up, while late-flowering (mid- to late summer and autumn) clematis should be pruned hard in late winter.
This group contains the vigorous, late- spring-flowering, Clematis montana and earlier blooming evergreen, C. armandii; the late-winter-flowering C. cirrhosa, and dainty C. alpina and C. macropetala which both flower in mid-spring. These need little pruning once established, except to remove dead and damaged stems. After flowering, remove any wayward shoots and damaged growth. This also helps to reveal the attractive fluffy seedheads.
This group includes the flamboyant large-flowered cultivars, like ‘Nelly Moser’. Wood made the previous year bears flowers in early summer, but these plants can also bloom again in late summer on stems made the same year. In early spring, follow the stems from the top down to new growth, and cut just above it. Remove the dead and damaged tops of the stems, which will look brown and dry, and cut back to green buds from which flowering side shoots will grow.
Clematis that flower from midsummer through to the autumn make up this group, and include the prolific small-flowered C. viticella hybrids, and forms of C. texensis. The yellow autumn-flowering C. tangutica and C. orientalis also belong here.
When left unpruned, these clematis form flowers at the top of the plant, leaving long, straggly bare stems beneath. To prevent this, cut back the tangle of shoots, removing them from their supports. Do this in late winter before the buds have started to break.
Then cut all the stems back hard. It may look drastic, but pruning the stems to within 12 in (30 cm) of the ground encourages plants to develop a strong network of new shoots. Cut to just above a pair of healthy buds. Prune less radically if you want to maintain height.
Excerpted from How to Grow Practically Everything
© Dorling Kindersley Limited 2010