Perennial vines like clematis benefit from some form of pruning. Clematis vines come in all shapes and sizes but did you know they also come in different classes? Classes indicate the time and method of pruning and are dictated by when the plants bloom and from which wood the buds form. When you purchase a clematis there should be a tag that indicates to which class the plant belongs. If you inherited a clematis and have no idea what class it is it can be confusing when confronted with that tangle of vines. One clue might be the appearance. If the vines are excessively heavy at the top with little green or blooms on the bottom, it might be a Class 3. If you have blooms all season long, you probably have a Class 2, where flowers are formed on both new shoots and old wood. Early bloomers are likely a Class 1 and need an entire season for young growth to mature and form flowers.
Experts recommend pruning all new clematis as Class 3 in the first 1 to 2 years. This promotes a fuller plant but can result in limited blooming initially. Class 1 plants flower in early spring off of the previous year's growth or old wood. These plant require pruning after flowering. The vines should only be lightly pruned to remove dead wood and control growth. If necessary, revisit the plant the following spring and remove any material that hasn't gotten leaves. Be careful not to cut into the very old wood, the base "heart" of the plant. If you damage the oldest stems, the plant may just decide to give up the ghost and not come back at all.
Class 2 clematis form flowers in late spring to early summer and will produce blooms occasionally through the summer on new shoots. In late winter or early spring, do a light pruning that thins the plant and takes vine material back 1 foot to a healthy, vigorous buds. After the initial growth, take the plant back by 1/3 to promote a thicker flush of growth. You will still be able to enjoy the later blooms which will form off the new shoots. Clematis in the Class B group that are overgrown will benefit from a drastic pruning. After the initial bloom, cut the plant back to 1/2 it's size. The next season will not require any pruning. You can use this pruning method in alternate years for really vigorous growers or those that you need to keep to a minimal size.
The final class, Class 3, blooms on new wood. These plants are for the fearless gardener who boldly chops without reservation. Class 3 clematis need to be cut to a foot above the ground in late winter or very early spring. The group blooms in late summer or fall and early pruning will result in easier training as the plant develops new vine growth over the summer season. It also forces a thicker lusher plant. Prune them back to a set of strong buds.
As with any pruning practice it is important to use clean, sanitized, sharp tools for the project. Clematis wood can splinter easily and requires well honed shears. You also want to avoid spreading and diseases from other pruning projects. If you are still confused about how to prune your clematis it won't hurt to do nothing but your vines may get out of hand. You can also chose to do a drastic pruning every 3 years or so, but be aware you may sacrifice some flowers the following season. Clematis are such spectacular plants that a little confusion and work are a small price to pay for an abundance of wildly colored blooms tumbling over themselves in happy profusion.