There are three different groups of clematis. Some like to be cut to the ground each year. Others just need a simple shearing to keep them looking good. The key to success is figuring out which of the three pruning groups your clematis belongs to. If you are unsure, let the plant grow freely for a year or two and watch how it flowers. You will then be able to assign it to a group.
Spring bloomer on growth from previous year –prune right after they finish blooming in spring. This will allow new stems to make flower buds for the following year. How much to remove? Depends on how vigorous the vine grows—some can be cut back almost to the ground, like C armandi. Others need very little pruning, like C. alpina and C macropetala and other slow growing varieties. No matter how you prune Group 1 plants, the new shoots that appear after pruning are the ones that will bear flowers the following season. Some Group 1 members are: C.alpina; C.armandii; C cirrhosa; C macropetala; and C. montana
Repeat Bloomers—bloom in late spring or early summer, then bloom again on new shorts and old stems. The vines that bloom mostly on older stems have their heaviest flush of flowers in late spring, while those that bloom mostly on new shoots are more prolific in the latter part of summer. It is best to lightly thin out and disentangle stems before growth begins in late winter or early spring, and then go over the plant again after the earliest flowers fade in late spring or early summer. Severely shorten the stems that bore those flowers. OR, another option is to severely prune the plant back by half its size alternate years—but you may give up the earliest blossoms in the season you prune.
Some Group 2 members are: C.florida; Bees Jubilee;Elsa Spath;General Sikorski;Henryi;Nelly Moser; Niobe;The President;Will Goodwin; Vyvyan Pennell.
Summer or Fall Bloomers---flower in late summer or in fall, on new growth produced earlier in the season. These are the easiest vines to prune—just before the seasons growth begins, prune all stems back to strong buds within a foot or so of the ground. If you want your late bloomer to ramble up into a tree where you want its blossoms held high do not prune heavily. OR, you can do the almost nothing method and long as you don’t mind an unmanageable vine. A drastic pruning every few years may sacrifice some blooms in the short term, but it will bring the plant to a more manageable size. Some Group 3 members are: Comtesse de Bouchaud; Ernest Markham;Gipsy Queen; Jackmanii;Lady Betty Balfour;Perle d’Azur;Ville de Lyon.