Pruning clematis is important especially during the first two or three years after planting.
All newly planted clematis, regardless of group, should be pruned down to 300 mm (12”) during their first spring.
To try and alleviate the apparent confusion surrounding the pruning of mature clematis just remember that most fall into one of three groups.
If you don't know the variety or group, wait until the plant flowers then prune accordingly.
Listed below are details on the pruning and flowering period of each group;
Is made up of Clematis alpina, C. cirrhosa, C. macropetala, C. montana cultivars and other early small flowered species.
These flower from January - May on shoots produced the previous summer.
Generally there is no need to prune these varieties, an occasional tidy up is often all that is required as this will encourage production of new growth to flower the following season.
Winter damaged growth should be removed in spring, and over-long shoots, should be cut back to healthy buds after the plant has flowered.
If you consider the plant/s is too large, then cut it back after flowering.
That is remove any dead, diseased or damaged growth and hard prune the stems back to 150-300mm (6"-12") from the base.
Subsequently new growth can be trained in to the space available.
These are deciduous large flowered cultivars such as C. Nelly Moser.
They flower flower through from late spring to early summer on side shoots from the previous years growth.
They may also flower mid to late summer on the tips of the current year’s shoots.
Pruning should be done before growth begins in early spring circa Week 13>
Simply remove dead, diseased and damaged growth and trim all remaining stems back to the nearest strong bud.
These buds will then create the framework of second year shoots that produce side shoots that will flower in late spring and early summer.
The young shoots may then bear further flowers later in the summer.
If some serious renovation is required then these plants can be cut back hard to 150-300mm (6"-12") in spring every few years.
Early flowers may be lost by this but the second flush will be enhanced.
This is quite a diverse group that includes large flowered cultivars, small flowered species, C. tangutica and C.viticella, plus the herbaceous group C. heracleifolia and C. integrifolia.
These all flower from July - October on the current year's growth, so pruning is simple: cut all stems to a pair of strong buds 150-200mm (6"-8") above soil level before growth begins each spring, circa Week 13>
Small-flowered clematis with attractive seed heads such as C. tangutica can go unpruned, and thinned in spring when they outgrow their space.
Prune back old unsightly Viticella shoots in autumn when they can be pruned hard to within 300mm (12") of the ground.
However it is far better, particularly if they are being grown through tall shrubs, hedges and trees, to prune them to around 900-1200mm (36”-48”) high in late winter/early spring.
Cuts should be made just above the swelling buds on shoots that lie in the direction you want them to grow.
Viticellas grown along the ground can be pruned back to around 1500-2000mm (5’-6’) .
Pin the ends of the shoots to prevent them blowing over each other and to lead them in the direction you want them to grow.