MANY varieties of clematis need cutting back now. Given a brief spell of mild weather, they come quickly into growth, producing fresh green shoots which will go on to flower later in the year. Rather, than cut away all this young growth in March, prune now.
The clematis which urgently require this treatment, cutting back to about a foot or so from ground level, are the viticella group and the jackmanii group. These flower after mid-summer on new growth produced in spring and early summer.
Spring and early summer flowering clematis flower on last summer's growth so these should not be pruned now. True, some of these become a tangled mess, resembling a huge messy and untidy birds nest. Those who cannot endure such a sight can try to tease out and tidy the plant a little. Sometimes the only solution is to prune as much as is necessary to restore order and to suffer the consequences - far fewer flowers in the coming season.