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Herbaceous Clematis

Most gardeners know what they want from a plant. Delphinums must be blue, sweet peas be scented, and dahlias be bold and blousy. Red delphinums, unscented sweet peas, and dwarf, modest dahlias might excite plant breeders but do nothing for most of the rest of us. This preference for plants that display their fundamental nature can lead us, though, to disregard some first-rate garden plants.

Clematis are one of British gardeners’ favourite plants, as the one-thousand-or-so varieties listed in the RHS’s Plant Finder testify. Our expectation that these should be showy climbing plants has led to the non-climbing, herbaceous forms of clematis being overlooked. In his important early book on clematis, written over thirty years ago, Christopher Lloyd skips through the group in half-a-dozen pages. Recently, however, clematis-breeders have recognised the value of these plants, particularly for smaller gardens, and many new varieties are being introduced. Hardy, disease-resistant and with a long-flowering period that is followed by attractive seed heads, herbaceous clematis can be staked or allowed to scramble through other herbaceous plants and shrubs, grown in pots, or allowed to sprawl over low walls.

The shoots of C. recta are the first to appear: slender as asparagus and with the force of peonies, they thrust though the soil in April. The stems grow to about 1.2m long and, left to their own devices, will scramble along the ground and push up through adjacent plants. Grown against a wall or fence the plant will lean back for support like a tired gardener. A froth of small white narrow-petalled flowers appears in June which, though individually unremarkable, are, en masse, a glorious scented cloud. The flowers are followed by pom-poms of silvery plumed seed heads typical of the whole genus.

Lloyd wrote that he found the C. recta tiresome and suggested that gardeners not bother with the species but should grow C. recta ‘Purpurea’ instead. The new growth of this form should be a luxurious, rich-purple colour which fades to dull-olive by midsummer. Most of the plants sold under this name are now seed-raised and the eye-catching stems that Lloyd described are not as intensely purple as they seem to have been thirty years ago. Two recently-introduced cultivars, C. recta ‘Velvet Night’ and C. recta ‘Lime Close’ do, however, have purple shoots and leaves that remain that colour until late July, when they begin fade to a smokey-green. I grow both cultivars and can see little difference between them. Mine grow through a perennial wallflower with sparkling amber and apricot flowers, Erysimum ‘Apricot Twist’, and are supported by a very old white-flowered rose. Metal or wicker frames are a good way to support the plant if you don’t want it to straggle along the ground but don’t truss it up: allow the plant to support itself naturally. There is a magnificent specimen of C. recta ‘Purpurea’ at Stoneacre, the National Trust garden in Kent, where it is grown over a willow frame and surrounded by Helianthus, Echinacea and other late-flowering perennials.
C. integrifolia has much more flamboyant flowers than C. recta. On the species these are sweetly-scented indigo-blue bells that open from buds that resemble the neck and head of a swan. The tepals twist back as the flower ages. Native to southern Europe, it has been grown in Britain since the mid-sixteenth century and has produced dozens of cultivars that range from white to dark blue and from pale pink to deep burgundy. The stems grow to between 60cm and 1m, depending on the cultivar, with a single flower hanging from each from June to August. Of the blue-flowered forms, C. integrifolia ‘Ozawa’s Blue’ has mid-blue scented flowers with tepals that corkscrew and darken with age. C. integrifolia ‘Budapest’ has much darker blue flowers that are very attractive scrambling through the lower branches of Elaeagnus ‘Quicksilver’, whose scented flowers make up for this cultivar’s lack of perfume . One of the best pink forms is C. integrifolia ‘Hanajima’, darker on the outside of the tepals, and with a pale pink, softly-textured interior.

Clematis integrifolia has been hybridised with other species and with large-flowered clematis to produce compact plants with more conspicuous flowers than are usually found on integrifolia cultivars. From the Ukraine, C. ‘Alionushka’ has 6cm wide deep pink flowers that have a darker rib down each tepal. Ten years ago it received the British Clematis Society’s Certificate of Merit. Much larger purple-blue flowers smother the 1.5m stems of C. ‘Arabella’. The tepals are much broader and rounder than the species and the flowers are open and upward-facing.

While most herbaceous clematis need support to keep them upright, C. heracleifolia, from northern China, has strong stems that need no propping up. The large leaves of the species can often obscure the plant’s clusters of perfumed mauve flowers but several cultivars have been selected with plants that are much more apparent. On C. heracleifolia ‘Cassandra’ the sprays of flowers, which individually resemble a hyacinth, are pale blue. The cultivar ‘Chinese Purple’ has much darker blue flowers which appear even more attractive against the plant’s dark stems.

Thought to have C. heracleifolia as one of its parents, C. Praecox is unsurpassable as a ground-cover plant. The three-metre stems, that become woody with age, cavort quickly in all directions and are smothered with clusters of small mauve flowers from late June to September. As the flowers age they begin to sparkle with prominent pale-yellow stamens. C. ‘Mrs Robert Brydon’ is a similar hybrid with pale-lavender flowers. Both are robust plants that I have seen growing in very shady situations as well as in full sun. In mild winters the stems do not die back and the plant can look withered and untidy by the spring. If this happens shear the plant back to healthy growth , or even to the base.

In the past decade there has been an explosion in the number of herbaceous clematis produced by clematis breeders in America, Japan and eastern Europe. In my garden the most floriferous of these new varieties is the ‘Prairie’ series , introduced in Britain by the Guernsey-based clematis-breeder Raymond Evison. C. ‘Medley’ has narrow-petalled magenta-pink flowers that are each 4cm wide and slightly scented. Another in the group, C ‘Gazelle’, has slightly larger, pure white flowers with twisted tepals. Both plants grow to about 1m tall and are smothered in flowers throughout the summer.

The perfume of the scented herbaceous clematis tends to be muted and delicate but, as its name suggests, C x aromatica has a scent to rival anything Chanel has produced. Its by far my favourite herbaceous clematis and if you only have space for one plant, this is the one to grow. The dark purple tepals of the flower furl round to reveal an explosion of cream anthers that make the flower as attractive as its perfume.
Clematis are members of the Ranunculaceae family of plants that includes buttercups, aconites, thalictrum, anemones and hellebores. Looking closely at the individual flowers of these plants reveals the similarity in flower-shape to clematis flowers. Most flowers consist of an outer green sepal, that protects the bud and the flower, and a circle of coloured petals that attract pollinating insects. Clematis flowers differ in that the sepals are brightly coloured, doing the job of both sepals and petals and are known as tepals.

Clematis recta is used in homeopathy under its former name of Clematis erecta. The sap from crushed leaves is homoeopathically prepared to treat several ‘men’s problems’ such as urinary tract infections and irritable or swollen testicles. It is also used to treat people “lost in sad thoughts, and in apprehensions of impending misfortunes, sullen and out of humour”.

Herbaceous clematis need to be grown in good, well-drained soil in full sun or partial shade. On the whole they are tough plants that do not suffer from specific pests or diseases. They are not susceptible to clematis wilt, which can affect climbing clematis, although the new shoots of C. recta seem to be very attractive to slugs and snails. Clematis integrifolia can be cut back to the ground after it has finished flowering, and will produce a second batch of flowers.

The clump-forming forms can be divided in autumn or early spring in the way other herbaceous plants are. C. heracleifolia and C. recta can also be propagated from cuttings that are taken from the base of the plant. Clematis cuttings are very prone to wilting and to botrytis, so keep them shaded from the hot sun, do not over-water them, and do not crowd them together. C. recta and C. integrifolia are easily grown from seed but the offspring may be very different from the parent plant.