There's nothing more spectacular than a clematis in full bloom. Who doesn't dream of trellises covered with vibrant red or rich purple flowers in late spring? Even as the blooms fade, they leave spidery seed heads. And fall just wouldn't be perfect without sweet autumn clematis' intoxicating fragrance.
But how do you get your clematis to grow lush and beautiful? If you've grown clematis, you know that pruning can be puzzling. The fact is your clematis will survive and bloom with no pruning, but with the right pruning it'll grow and bloom more vigorously.
Timing is important. Don't prune in the fall. No matter where you live, its best to let your clematis stay unpruned and dormant until spring. You'll first need to know which pruning group your clematis is in, A, B or C (sometimes called 1, 2 or 3). If the tag doesn't tell you just watch it for a year. First, pay attention to when it blooms. Second, notice whether it blooms on woody stems that grew last year and then survived the winter (old wood) or green, flexible stems that came from a main stem this year (new wood).
Pruning Group A (or1)
If you have a clematis that doesn't die back in winter and blooms early in spring it's probably a Group A cultivar. This group only needs enough pruning to keep plants looking fresh and under control.
Since these clematis bloom in early spring on old wood (produced the previous season,) wait to do most of your pruning until after the main flowering has finished. Prune too early and you'll be cutting off the flower buds.
Winter can sometimes kill back the tips of Group A clematis. If that happens you'll need to do a bit of pruning earlier than normal. Prune from the top to a spot where there is green under the brown outer layer of bark.
Any Group A clematis that is not flowering well or has overgrown its spot probably is due for a renovation pruning. After the vines flower cut off almost all of the side branches leaving only the main vertical stems that fasten the plant to the trellis. Don't cut the plant back near the ground.
Pruning Group B (or 2)
Large-flowered doubles and rebloomers usually fall into group B. Most doubles produce double flowers on old wood and single flowers on new wood.
Heights of group B clematis can vary almost as much as those in group C. Most grow 10 to 12 feet tall and make excellent subjects for covering
structures such as pergolas, arbors, fences and trellises. Look for a structure with plenty of cross pieces no more than about 6 inches apart so the vines can climb from one to the next. Make sure it's tall enough; otherwise, when the stems reach the top they have nowhere to go and tend to flop over into a tangled mess.
Group B cultivars are good companions to roses because their pruning requirements are similar. As plants leaf out in spring remove any stems that have died back and then do a light pruning to keep both vines trained to their structure. Group B also includes a wide range of colors. The large flowers open in spring on old wood. By late summer the new wood produces smaller flowers about half as large as the earlier ones.
Pruning Group C (or 3)
Group C has cultivars that bloom in spring or summer as well as fall. Many of these in-between sized cultivars are great for growing on obelisks or trellises or training into small trees or shrubs like lilacs or viburnum. These clematis are large enough to show up but not so big that they'll smother the shrub.
This large group of clematis has lots of different heights to choose from. Sweet Autumn is one of the tallest at around 20 feet. Provide a large structure to climb on or use as a groundcover Any group C cultivar can be used as a groundcover. Flower sizes in group C vary greatly. If your clematis dies to the ground over winter or if the flowers are only at the top with lots of last year's dead foliage and bare stems showing at the base it's probably a C.