Pruning Clematis is one of those areas where hesitation is often due to unfamiliarity with the particular plants’ needs rather than any lack of skill. However, there are a few simple rules which even if they get forgotten, are easily re-learnt and applied.
The first thing to ask is whether the Clematis is one of the herbaceous types or a climber. I have seen Clematis divided into as many as eight groups for pruning purposes – which is somewhat excessive and confusing too!
Whilst there are numerous Clematis species, hybrids and cultivars to choose from when planting, for pruning purposes established plants can be split into three distinct pruning groups. These are based on the flowering time and the age of the flowering wood – which should help you to work out which pruning group a Clematis falls into if the plant label or planting plan has been lost.
To be doubly sure, wait until the plant has flowered. If the Clematis flowers before early summer, around June, do not prune it. Whereas if it flowers from late June onwards, prune in late winter, ie February, although not on frosty days. Herbaceous Clematis fit into late flowering group.
General pruning note re newly planted Clematis
Young plants should be hard pruned the first spring after planting, to about 12 inches above ground, unless there are already 3 or 4 healthy stems growing from the base. This encourages healthy stems and flowers. Feed and water after pruning and tie in new growth for even spacing of stems on their support for better air circulation.
Containerised mature plants should be pruned as per normal, although some pruning on planting may be necessary. For example, to remove any damaged stems.
Group 1 Clematis – ‘no pruning’
These flower early in the year on shoots produced in the previous summer. C alpina and evergreen Clematis such as C. Armandii fall into this category.
They do not generally need regular pruning, except for dead heading. But if necessary, then lightly prune immediately after flowering in mid to late spring when the danger of frost has passed. Remove winter damaged stems and overlong branches back to a pair of healthy buds.
Where a plant has seriously out grown its allotted space, it is advisable to take a couple of seasons to reduce its size or risk killing the Clematis. The exception are the vigorous C. montana, which will tolerate being sheared back after flowering to keep them in their allotted place.
Group 2 Clematis – ‘light pruning’
This group comprises the early large flowered Clematis including the double and semi-double cultivars. For example, C. ‘Nelly Moser’, Clematis florida var. sieboldiana.
These flower May to June on short shoots which develop from the previous year’s growth. Some will flower again in late summer on new growth, which can be encouraged by cutting back to a strong bud or side shoot.
Generally, these Clematis only require the flowers to be cut off, back to a large growth bud immediately below the spent flower as soon as flowering is over.
They can, if preferred, be left unpruned except for the removal of dead shoot ends in late winter or early spring. This is also the time to remove dead or weak stems before growth begins. Follow spindly or damaged stems from the top down until you reach a pair of healthy buds and prune just above these.
After the first flush of flowers is the time to cut back a plant that has outgrown its position or become a birds nest of a tangle at the top. This is achieved by hard pruning down to a strong bud, and they are unlikely to produce a second flush of flowers that year. Reducing the plant over two or three seasons rather than in one brutal prune is generally best.
However, an alternative method is to hard prune them to 1–3 feet from the base every three or four years in late winter. They will only flower once in the year following renovation.
There’s always one…
Some mid to late summer flowering clematis can be treated as either group 2 or group 3. For example, C. ‘Jackmanii’, C. ‘Perle d’Azur’.
If you’re not sure which would be the more suitable pruning technique, then observe on which wood the flowering occurs as well as when in the year. This will help in the decision. Generally speaking, combining the pruning methods for groups 2 and 3 by retaining a basic framework while cutting other stems to the base works well. And it has the added benefit of extending the flowering season.
Group 3 Clematis – ‘hard pruning’
This group flower on the new season, ie current year’s growth. It includes, for example, the late large flowered hybrids and the small flowered C. viticella, C. orientalis.
As growth continues from where it ended the previous season, an unpruned group 3 Clematis ends up a tangled mass of growth, flowering well above eye level with bare stems at the base.
These plants need to be regularly hard pruned in late winter or early spring when buds show signs of growth, usually February.
The easiest method is to start at the bottom of the plant and work your way up each stem separately to the first pair of healthy buds. Prune the stem above these buds. By treating each stem in a similar way, the Clematis will be encouraged to put on strong new growth and a good floral display.
NB
Some of the small flowered group 3 Clematis have attractive seed heads, for example, C tangutica. If these are still looking attractive, then the plants can just be trimmed back to the main framework of branches, allowing the seed heads to be enjoyed for longer.
Herbaceous Clematis
Herbaceous Clematis such as C. recta and C. integrifolia should be pruned nearly to ground level in late autumn or early spring.
To recap
When deciding when and how to prune a Clematis, observe when it flowers – early, mid or late season – and on what age of wood.
Marie Shallcross
Plews Garden Design and Consultancy