In this step-by-step guide, learn how you can keep your clematis strong, tidy, and heavy-blooming starting with training a new plant you just bought and working through to an old giant that needs rejuvenation. We'll start with the things you need to think about before you even make the first cut.
Before you prune, you need to know your variety or at least the time of year it flowers. Flowering time will determine when and how to prune it both to promote flowering and to train the plant’s “frame.”
Also choose your clematis’s armature—the trellis, arbor, wires, or other structure and shape you will make it climb on. You can have it scramble on the ground or over rocks for a wild look, but you will still need to set off space for it and eventually control it to that space.
Establish Your New Clematis
Promote establishment by cutting back hard at the end of the first winter. If your new plant is a mature (bloom-ready) and early spring-flowering variety, you can wait until just after flowering if you can’t bear to sacrifice the blooms.
You can repeat the practice of cutting back hard for the first few years or cease the practice after just the first winter.
Training Clematis: Build A Frame
The goal of training is to develop a strong basic “frame” of strong wood in the space that you want your plant to occupy. Wood in the frame of the plant lasts many years and should be much smaller than the total plant size you are aiming for because many feet of new growth will sprout from it every year.
By frame, we do not mean the armature, which is a man-made structure.
Early Spring- to Summer-Blooming Varieties
As the plant grows, prioritize a small, odd number of strongly-growing stems, perhaps five. Train them in the right direction by tying or guiding these around the armature. These stems will become your permanent frame bearing the rest of the plant. The frame canes last from year to year, to be cut down only in occasional renovation pruning.
Because you will cut these back nearly to the ground, the year-to-year frame is nearly nonexistent—just stubs around a foot high or less.
Maintaining Clematis: Yearly Pruning
In late winter cut off all dead, diseased, and damaged wood. As in all fast-growing plants, clematis produces a lot of weak wood that will be killed by winter. Gently wind any cut wood out of the plant mass.
Early Spring Varieties
Tidy these after they flower. After the flowers fade, cut weak floppy growth back to a strong bud on a strong, stable part of the plant on or near your frame. Since clematis grows so quickly, you may well have to cut back many feet of growth until you get to the frame—most years you will cut all or almost all of last year's growth, and on old large plants, you may need to use shears rather than secateurs to be efficient. Remember your initial plan for the plant’s size and stick to this! Don’t let a fast-growing vine tell you how big it should be. Be brave and methodic, keeping your target size in mind.
Mid- or Late-Spring Varieties
In late winter, before new growth begins, cut back all canes to a strong bud, but leave some of last year’s growth where you can. Go for cutting near the frame, but not quite to it. Why? The tips of last year’s wood are the weakest, but the wood just behind this will bear the flowers. Winter often kills tips and even those that live come through internally damaged and weak. Cutting back now rebases growth from strong wood.
This type is the hardest to prune right because you need to strike a balance. Learn to tell last year’s wood from older wood and aim to cut back to the first few strong nodes of last year’s wood. You’ll often be cutting a couple of feet, even three feet of growth on each cane.
By the way, these varieties are also the ones you can deadhead to encourage reblooming.
In late winter, cut all canes back hard to healthy buds, leaving a base of strong old wood just a few buds high above the soil. These are probably the easiest types to know how to handle.
Older Clematis Vines: Renovate Yearly
When your clematis reaches full size, mature and in its place for perhaps three or more years, parts of your frame will need to be cut completely down every so often—this is renovation pruning.
To renovate, choose and completely cut out the oldest third (or so) of wood, even if it still alive and strong-seeming. You do this to get the plant to regrow new, vigorous wood from the base a little at a time each year—it’s rather like putting the plant on a kind of physical fitness regimen.
Renovate at the same time you would do your yearly pruning above. Remember that this is thick old wood, so use loppers or pruning saw. As you cut, be careful with the canes nearby: all the bases will be squeezed tight together and you don’t want to cut into the ones you are leaving behind.
During the Growing Season, Manage New Growth
Now that you have done your major pruning early in the growing season, the plant’s frame or stumps will produce many feet of new growth over the course of the year. Through spring and summer, guide and tie this growth to your armature to keep the plant tidy-looking and its blooms well-supported where you want them.
Source for all steps: Gooch, Ruth. Clematis The Complete Guide. The Crowood Press, 2001