Guidelines for pruning the 3 Groups of Clematis.
Group 1: No Pruning
The varieties in this group of winter and spring flowering bloomers require no pruning; members of the Atragene Group, Montana Group and the Evergreen Group. If you need to keep the plant tidy, cut out dead or broken stems, or for general upkeep, trim after the main period of flowering. This will allow the plant enough time to produce plenty of new growth that will provide flowers next year.
Group 2: Light Pruning
A. Newly planted young, large-flowered plants from this group should be pruned hard on planting and then one or two times before flowering. Again in late winter/early spring for the first two years after planting, as this helps to establish a strong root system.
B. For established plants, prune in late winter/early spring when the buds begin to swell and you can see what wood is alive. First, prune out dead and broken stems. At about one-third of the height, prune just above a strong pair of buds on each stem. Separate the stems and tie to a support. After the first period of flowering is finished, give the plant another very light pruning and fertilize. This will help promote another round of blooms.
Group 3: Prune Hard
This includes the late, large-flowering hybrids, late flowering species, the Viticella Group and the Herbaceous Group. They all bloom on the current year's growth (new wood) and require hard pruning in early spring when the buds begin to swell. Starting from the base of the plant, prune just above the second pair of buds. If the plant is herbaceous, it may die back to the ground and if it's woody at the base, prune to a pair of strong buds just above the ground.