Plant of the Month

June 2004

Herbaceous Clematis
by Mike Brown

Clematis integrifolia © Mr. Ian Lang

Although still not as well known as their climbing relations, many excellent, fully hardy and trouble-free herbaceous clematis are now appearing at garden centres and specialist nurseries. Some are selections of Clematis integrifolia itself, occurring in various shades of white, pink, blue and purple, with small but beautiful, nodding bell-shaped flowers. Mostly clump forming, they will reach about one metre, height and spread. Others are usually interspecific hybrids where one of the parents is C. integrifolia and the other something very different. This second group includes a much wider range of bloom shapes and sizes as well as considerably larger plants, sometimes in excess of 2.5 metres.

Clematis stans © Mr. Ian Lang

There are a few scented plants among herbaceous clematis, notably C. heracleifolia and C. stans. The sunnier the border, the greater the scent. All herbaceous clematis are summer blooming, some starting in May, most in June and often, quite a few of them will still be in flower in October. Plants such as C. 'Arabella' and C. 'Alionushka' will bloom profusely and continuously for four to five months.

Clematis 'Alionushka' © Mr. Ian Lang

When grown in a mixed border, it is often possible to combine them with spring blooming shrubs, which will act as natural supports for these herbaceous beauties. Some will completely envelope a twig bower, (used to good effect each year at the Royal Horticultural Society garden in Wisley, Surrey, UK) while others are best left to wander, unfettered, wherever they choose, their flowers suddenly greeting the gardener from the most unlikely places.

No single plant supplied in a 2-litre pot is going to give a high impact in its first season but three of them, planted close together will, for sure. A versatile aspect of herbaceous clematis is the ease with which their height can be controlled. The same named clematis can be allowed to reach 2 metres if being grown with similar sized support plants or shrubs, or, kept at no more that 1 metre if it is to be placed near the front of the border with much shorter companions.

Clematis 'Fascination' © Mr. Ian Lang	Clematis x bonstedtii 'Campanile' © Mr. Ian Lang

This height control is achieved in two ways, either by double or triple pruning of the whole plant, or by repeated pinching out of growth tips after just two or three pairs of leaves have been made. Multiple pruning is the normal ground level pruning at the start of the season, followed by further pruning of all shoots back to one or two nodes, if done once but then back to one or two nodes on this new growth if done again. The period between successive pruning with this method depends on climatic and geographic conditions, as well as the availability of time. Pinching out will delay blooming by about five or six weeks - so can be timed to permit flowering to start as you return from your holiday.

Basic pruning is the simplest for all types of herbaceous clematis. Plants can be tidied up with the normal border work in late autumn, reducing stems down to 30cm, and then right down to ground level in late winter (usually February in Britain and Ireland) when new basal shoots have appeared from below ground. Failure to prune severely enough will result in weak, straggly growth and poor quality flowers. Despite growing herbaceous clematis since the 1960s, I am still awaiting my first confirmed case of clematis wilt (stem rot). Herbaceous clematis are impervious to clematis wilt. Like other ornamentals, herbaceous clematis can eventually be killed by total neglect or serious pest infestation or disease but they are much more tolerant of less than ideal conditions than most other types of clematis. No real mixed border is complete without a few such treasures.

Clematis 'Pamiat Serdtsa' © Mr. Ian Lang

Seek and find some of the following plants:

C. 'Arabella', C. x bonstedtii 'Campanile', C. x diversifolia 'Olgae', C. tubulosa 'Alblo' (Trade designation: ALAN BLOOM), C. 'Pamiat Serdtsa', C. 'Pangbourne Pink', C. 'Sinee Dozhd' (Trade designation: BLUE RAIN), C. integrifolia, C. integrifolia var. latifolia, C. 'Alionushka', C. x cylindrica, C. 'Fascination', C. 'Tapestry', C. 'Fascination', C. 'Côte d'Azur', C. x durandii, C. 'Evisix' (Trade designation: PETIT FAUCON)
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