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Last updated 26/3/20 10:28.
Clematis - Growing Guide
There are so many types and forms of clematis that growers can easily become totally confused as to when and exactly how to prune them. To make life simpler and more easily understandable clematis species and varieties are split into three distinct pruning categories.
If left unpruned clematis can quickly grow into a mass of tangled stems with a bare base and all the flowers appearing well above eye level at the top of the plant. It is not unusual for the trellis or structure supporting your clematis to collapse or fall away from the wall with the weight of several years’ new and old growth. Pruning encourages new growth which will very definitely increase the number of flowers in the following year.
Pruning can also keep your plants healthy. Clematis wilt or clematis rot usually appears in early summer causing the plant to collapse and turn brown. Although there are reasons other than inadequate pruning which encourage these occasional diseases, proper pruning will certainly reduce them by cutting out weak or excessive growth back to new healthy tissue. More light and air flow will get to your plant which may well have been one of the causes of the original problem.
Pruning Group 1 - Flowering mid / late spring
Clematis should be pruned in mid to late spring after flowering and once the risk of frost has passed. This might be termed as ‘tidying up’ pruning.
These clematis bloom early on shoots produced the previous season. How much you decide to prune depends on the vigour of your plant and the size of the support that it is growing on.
Vigorous growing varieties, and in particular, C. armandii, relish being cut back hard and even to ground level. Conversely C. macropetala varieties grow more slowly and pruning can be just a tidy up. C. montana varieties do not readily shoot from the old wood so pruning needs to be gentler and careful here.
Whatever you do to Group 1 plants they will have the whole season left to grow the new growth on which the flowers will appear the following spring. What you are doing is tidying and preparing your plant for that.
C. alpina and cultivars
C. armandii and cultivars
C. cirrhosa and cultivars
C. macropetala and cultivars
C. montana and cultivars
Pruning Group 2 - Flowering late spring / early summer
These are clematis which flower in late spring or early summer and grow on again afterwards to flower periodically on new shoots and old stems. These are the category of ‘do very little’ or ‘do nothing’ as far as pruning is concerned.
If you cut these plants back after flowering you will stop them going on to flower progressively through the rest of the season so do not!
Certainly you can cut off the first flush of dead flowers to avoid the plant wasting energy in producing seed heads.
Certainly you can tidy up the plant before growth begins in spring. There may well be dead tips to cut out and old leaves to tidy up. There may also be stems from last year’s growth to thin out a little and train or tie in to new supports to grow in different directions. So a careful approach is needed but do not cut off too much!
C. florida and cultivars
Many large flowered hybrids including:
Pruning Group 3 - Flowering late summer / early autumn
These are varieties which flower in late summer or early autumn on new growth produced during the season. These are the easiest clematis to prune and you can be more drastic! The description is ‘prune hard’!
Flowers on these varieties are usually on the top two feet of the plant. If left unpruned growth will continue in the next year from where it left off in the previous autumn. This will quickly result in a tangled mess of growth with flowering at the top of the plant where it is difficult to see it.
So, just before the new spring growth appears, cut your plants right down to strong buds a foot or two from the base. Cut all the old growth from the trellis or supports and compost or burn it. It may well take a while to disentangle all the old growth which you have cut off but you will have a rejuvenated young plant which will grow away with great vigour. By mid summer it will be just as large and probably more floriferous than it was before you cut.
If you forget to prune your clematis hard for a year or two there is nothing to stop you getting back into action later. If you leave it too long to give your plant a drastic prune it may take a year before it recovers to flower well. Nevertheless it is still well worth doing.
The only exceptions might be where your clematis is happily climbing up a tree or over an old and unsightly building where a bare base and large trunks are a small price to pay.
C. integrifolia and cultivars
C. orientalis and cultivars
C. tangutica and cultivars
C. texensis and cultivars
C. viticella and cultivars
Many large flowered hybrids including:
‘Ville de Lyon’