We moved into a new house last spring, and there is an old clematis vine scrambling up and along a fence. It bloomed fairly well last year, but it looks to me like it needs some pruning – it has some pretty scraggly-looking sections in it. I don’t know what variety it is. How and when should I go about pruning it?
Clematis can be a confusing group of plants to prune, since they vary in flowering times, and therefore are not all pruned the same way. They are generally divided into three categories: clematis that flower in spring require little pruning (pruning group 1); those that flower in early summer require light pruning (pruning group 2); and those that flower from midsummer onward require hard pruning (pruning group 3). Without knowing which category your plant falls into, you may want to just do some renovation pruning this year, by removing most of the old, scraggly-looking growth, and retaining a few good long shoots. These may need fanning out and retraining, but your clematis should flower at some point during the summer, helping you to identify which group it belongs to.
Group 1 or spring-flowering clematis bloom in April and May from buds produced during the last growing season. Prune these plants immediately after blooming, but no later than the end of July in order to give the plant enough time to produce new buds for next year. Start by removing shoots that have bloomed; the only other pruning you will have to do is to remove any weak or damaged stems, or to control the size of the plant.
Group 2 clematis are the large-flowered hybrids which bloom in mid-June on stems from the previous season and often will bloom again in late summer on new growth. Remove dead or weak stems in late winter or early spring, leaving the best of last year’s buds. Once they finish blooming, deadhead all flowering stems or cut the plant back to 12 to 18 inches to force new growth for a second round of flowers.
Group 3 is made up of the late-flowering clematis, whose flowers are produced on the current season’s growth (these are the easiest to prune). In early spring, cut the plant back to 24 to 36 inches. Once the young shoots have grown to about 12 inches, prune half of them back to encourage more new shoots that will bear their flowers later than the first.