Identifying an unlabeled clematis right down to its particular species can be a challenge. With more than 400 cultivars worldwide, it is even more complicated than rose identification with about 100 species. Even if you can't pin the species down precisely with these tips, it is relatively easy to determine which of three basic pruning groups the plant falls into. This is important information to maintain your clematis properly.
Look at your clematis in the spring and check to see if the new growth is coming from shoots from the ground or from last year's stems. The species in Group 1 of the pruning groups, bloom on growth made in the previous year. Don't prune other than to remove dead foliage. Some Group 1 species of early blooming clematis include the Montanas, which are vigorous and can grow more than 30 feet tall and tolerate full sun. A common Montana variety, rubens, has light pink flowers and leaves with deep serrations; the stems appear purple in the winter. Other Group 1 cultivars include C. macropetala and C. armandii. Flowers can give you a clue as well as they are usually small, single and either saucer or bell-shaped. Chances are slimmer that your clematis falls into this group as it has the fewest number of varieties.
Examine your clematis' flowers. If they are large -- the size of a spread out hand -- they are likely a Group 2 variety. These varieties usually bloom in spring and then intermittently all through summer. Some in this grouping bloom in spring and then again in fall. Group 2 varieties bloom on new shoots from old wood and should be pruned lightly in spring to remove dead and damaged stems. This group contains the most number of varieties. Flowers are mostly saucer-shaped and can range from single to double. Some popular examples are Henryi, sugar candy, and Nelly Moser.
Watch for the bloom time of your clematis. If it blooms in mid to late summer, it is a Group 3 variety and could be Texensis, Viticellas, Jackmanii, or a member of the sweet autumn family such as C. terniflora. These clematis flower on new wood and should be pruned right back every year in winter when they are dormant to about 12 inches. These varieties grow quickly. You can identify a Group 3 clematis easily if it wasn't pruned the year before. It will look leggy, woody and won't have many leaves or blooms.
Ask an expert if you want to try and identify your clematis variety more specifically than determining its pruning group. Snip off a part of the vine with some leaves and at least one flower and bring it to your garden centre. Many cities and towns have clematis societies, as this garden climber is so popular. Garden books are another source of identification with full-colour photos of many of the varieties.
Once you identify which pruning group your clematis fall into, put a colour-coded tag on the vine or a stake in the ground. Keep a reference of your colour coding in your garden journal.