Proper pruning of Clematis

To prune or not to prune? a very frequent question we have. Keep in mind that a pruning done at the wrong time will not kill the plant but only delay flowering. Not pruning clematis doesn't mean that your plant will not flower it just minimizes the area and amount of flowering your clematis could otherwise flower.

Clematis usually refer back to three main pruning groups, A, B and C. Before pruning your clematis it is important to know what group you are working with to give the best possible prune to your plant.


Group A

These varieties will only produce flowers from the previous years growth. Pruning these should only consist of cutting out any weak or dead stems as soon as they are done blooming in May or June. If pruning any later happens, or pruning any harder down the stem, you risk the chance of having fewer blossoms the following spring. Popular varieties such as Macropetala, Montana and Alphina fall into this group, they can survive in colder climates but risk the chance of buds being burnt off by extreme frosts. Therefore blooms that should have occurred in early spring may flower in fall or not until the following spring.


Group B-1

These varieties flower on wood that has been hardened by the previous years growth. Normal blooming patterns for this group consist of heavy flowers in May-June on the previous years growth then followed by a season smaller flush of blooms in September on the current years growth. Nelly Moser is a fine example of a group B-1


Group B-2

These varieties simultaneously bloom on last year wood and this years wood. These varieties are commonly found to bloom from June- September continuously. For pruning purposes these varieties can be treated either as a Group B-1 or a group C and for that reason they work extremely well in combination planting with group B-1 or group C varieties. Great example would be Crimson Star clematis.

For both Group B-1 and B-2, in late March-April a light pruning with some variation in length of the stems will help produce a well balanced group B plant. Any weak or dead wood should be removed at this time. A severe pruning will reduce the number of blooms the plant will have next year, although a harder pruning may create a more balanced plant. If your Group B plant has been neglected for many years it can be rejuvenated by severly cutting back most of the old growth.


Group C

These varieties bloom on new growth from the current season. Flowers will start blooming in early summer and continue through into fall. These plants should be pruned back hard to three strong sets of buds on each steam as close to ground level as possible, in March- April. A pruning height of 12" from the ground is not uncommon. By pruning back this far will provide a plant with blooms that start near the ground level and continue to the top of the plant. The majority of the group C clematis start their new growth very close to where last seasons growth ended, so left not pruned they will very quickly grow out of control. Keep in mind that group C clematis bloom on current season's growth, so if they are left not pruned the blooms will be at the top of the plant and a bare stem will gradually appear over a few years. This could provide an opportunity to plant a lower growing group B variety to hide the bare stem and to extend the blooming season. Prince Charles is a great example of Group C clematis.


When to Prune
Pruning should be carried out at the following times:

Group 1, which needs little pruning, should be pruned immediately after flowering to stimulate renewed growth.

Group 2 is best left to early spring when the new buds are beginning to swell.

Group 3 can be pruned hard at almost any time during the winter and early spring, but some may also be part pruned in late winter down to new shoots as they emerge.
How to Prune

Group 1 Prune after flowering only if plants become overgrown. Clematis Montana should be pruned hard with caution, because thick branches sometimes do not regenerate.

Group 2 Look for large, fat buds, which are the flowering shoots. Thin out old growth and last year’s flowering shoots down to the fat buds, and retrain these as they grow.

Group 3 Prune hard to with-in 6-12in
(15-30cm) of the ground, but some shoots may be left alone then pruned later in spring to the new shoots as they emerge.
Twice-flowering Clematis, Group 2
This group includes all the large-flowered doubles and singles that flower in early summer and sometimes again later. They must be pruned lightly in spring.