A Brief Foray Into Clematis

The genus Clematis is a surprisingly diverse one, ranging from miniature alpine species to fairly giant herbaceous ones, with the size and growth rate of climbers varying between ‘friendly’ and ‘intimidating’, and there are a few that defy rational explanation too.

I could go on forever about the enormous range of Clematis species and hybrids around today, but mercifully for you I have other things to do so must limit myself to a few chosen favourites.

Like I suspect most gardeners, my first encounter with Clematis was one of the large flowered hybrids from a garden centre. I suspect it was probably C. ‘Nelly Moser’, that charming old variety that is usually the first answer when you ask a gardener to name any Clematis. It’s a good variety too, with bold striped flowers over a fairly decent season, by the standards of older varieties anyway, but keep it out of the hottest sun unless you like the ‘faded glory’ look in flowers. I grew mine up a wigwam in a hotchpotch border of roses, perennials and shrubs because that’s what you do when you’re new to gardening, right? The Clematis is long gone, but my interest in the genus has persisted.

Border Clematis tend to be referred to as ‘climbers’ or ‘herbaceous’; while ‘climber’ is pretty self explanatory, ‘herbaceous isn’t strictly speaking true, for ‘herbaceous’ Clematis are botanically ‘subshrubs’. While every gardener should be aware of this it’s common to find the non-climbing (non-alpine) Clematis referred to as ‘herbaceous’. Doesn’t really matter in itself, but it’s helpful to know that the ‘herbaceous’ ones will die back to a woody framework, particularly as they get older.

By far the best known of the herbaceous Clematis species is C. tubulosa. In the wild this species is found in scrubland, bushy slopes and the edges of woodlands in north western China. It’s mainly a plant for the late summer and autumn, and bears heads of unusual but recognisably ‘Clematis’ flowers of light or dark blue. This is not a ‘polite’ plant for a traditional border; its charm is a rough wildness, course leaves and a devil-may-care attitude to habit. Grow it with your pretty border plants and it will squash them out of spite, but grow it with robust forms of Japanese Anemone, asters, Persicaria amplexicaulis etc and you’ll be fine. This is a superb plant to grow with mature shrubs, particularly ones with good autumn colour.

Flowers of Clematis tubulosa

Now here we have a problem. This plant, as illustrated above, is commonly grown as C. heracleifolia, not C. tubulosa. They are quite different, however, with C. tubulosa having more upright heads of larger flowers, bunched together at the nodes. According to Grey-Wilson (2000) the majority of herbaceous Clematis cultivars belong to C. tubulosa. He also goes on to say that the plant commonly grown as C. heracleifolia var. davidiana is in fact little more than a somewhat more herbaceous form of C. tubulosa. Given that my other Clematis books make this error, even the usually infallible late Graham Stuart Thomas in his excellent ‘Modern Florilegium’ (‘Perennial Garden Plants’) and the late Christopher Lloyd in ‘Clematis’, this has every air of an error that has become entrenched in gardening, and will be hard to shake.

Thankfully Clematis stans has always been too obscure to be mistaken, although it did start its life as various varieties of C. heracleifolia before being put into its own species. C. stans is a Japanese species that occurs in open grassy habitats. Foliage-wise it is very similar to C. heracleifolia, but the flowers are easily distinguished by being very slender and almost a grey-blue.

“This is a floppy 1-1.3m herbaceous species carrying flowers of a spitefully non-contributory off-white, skimmed milk colouring. “Of little importance,” wrote Moore and Jackson. Hear! Hear!”

Christopher Lloyd, ‘Clematis’, 1989

So Christopher Lloyd wasn’t a fan then!

I think the main reason this species is so niche is plain to see; there is a lot of foliage for such slender flowers, and while the scent is charming it is also occasional (still not convinced that what I was smelling wasn’t a nearby Clerodendrum bungei). If I was recommending a species for the garden I would go with C. tubulosa every time. Whether I might afford C. stans a quiet corner myself, on the off-chance that it might suddenly become terribly exciting, I couldn’t say.

Clematis stans- not without charm, but does it have enough charm to be worth growing?

These herbaceous Clematis will never reach the dizzying heights of popularity enjoyed by the climbing species and hybrids. Partly this is due to their rugged looks, but also because the best forms are done from division (which can be challenging). Add to this the fact that they dislike being kept in check in the open border and you have three reasons why these plants are consigned to relative obscurity. I’ve long had my eye on a pink flowered Taiwanese species on the Crug Farm website, C. psilandra CWJ12377. When I tried to place an order I was told it’s out of stock, and best bought as a division in winter. This desirable species grows beautifully in the open ground, takes anything the weather throws at it, but keeping it alive in a container is rather more challenging. This is not atypical of these herbaceous species.

One climber that I doubt very much likes to be in a container for very long is Clematis vitalba. This is a very large growing species, best described as being a ‘rambling rose’ of the Clematis world! This species is found across southern parts of the UK, and right through central and southern Europe. In a hedgerow in Devon, UK, near me, there is a long stretch of this species growing wild; in summer it was a delight to see the hedges draped in white flowers, and now the seedheads are ripening and giving the hedges a new charm. I doubt this autumnal delight will survive much longer as we are a nation obsessed by the idea of tidiness and sooner or later a tractor and flail will be sent to cut the hedges. It was also a delight to see this species in patches along the A303 on my way towards London, scrambling through trees and fencing.

I first met C. vitalba at a client’s property, where it grows through the chainlink fence around a tennis court. Every year I cut it back to a framework of woody shoots at the base, and every year it grows to cover a vast area. In flower it is a delight, and seedheads are charming too (although they tend not to last as long without shelter). There are two disadvantages of it in this location though; firstly removing the brittle dead wood from the chain link fencing is a tedious but necessary job each winter, and secondly this species grows so densely that it tends to catch stray tennis balls and is reluctant to let go of them!

Clematis vitalba- likes ball games but is reluctant to share!

Given the sheer scale and rate of growth of C. vitalba it’s a wonder anyone would try to hybridise it, but in the early years of the 20th century C. x jouiniana was bred. Let’s be honest, any cross between the vast climbing C. vitalba and the ‘herbaceous’ C. tubulosa is going to be interesting; C. x jouiniana does not disappoint. Foliage-wise there is clear influence of C. tubulosa, as there is in the shape of the flowers individually. However, the general habit of the plant has a look of C. vitalba about it. The hybrid is nowhere near as massive as C. vitalba, reaching a mere 2-3m (6ft6 to 10ft) from a woody base (typical of both parents). Here’s the interesting thing though; it lacks the climbing habit of C. vitalba so it relies on being able to scramble through shrubs. It’s a non-climbing climbing Clematis!

Left to its own devices C. x jouiniana will scramble across the ground, over stumps or rocks, or anything else, only gaining height if it finds itself in the lower branches of a fairly dense shrub. By gardener’s intervention it can be tied to supports or draped over things, but this is a plant that needs a guiding hand and/or careful positioning to achieve its best. There is some discussion over the form ‘Praecox’, which flowers earlier (and finishes earlier) than the straight hybrid. It is often listed as simple Clematis ‘Praecox’- whether there is dispute as to its name I don’t know.

Clematis ‘Praecox’

The delight of this plant is the huge heads of large(ish) off-white flowers. The plant shown above is only juvenile and is I suspect unhappy where it is, but in another garden it can only be described as ‘bountiful’.

All of the Clematis described here are perfectly hardy across most of the UK, although whether they would necessarily achieve full potential in the colder areas is debatable. Certainly will survive winters in USDA z7. My suspicion is that in the warmer parts of the world, particularly the hotter parts of the US, many of the species Clematis could be a nuisance. However the whole genus is known for its dislike of hot conditions, preferring cool conditions at the roots if nothing else. I would guess that these species would struggle to survive the climate in most areas where non-native species have become problematic.

If you’re interested in Clematis can I recommend Clematis: The Genus by Christopher Grey-Wilson? It’s a superb book, filled with information particularly about the species. Second hand copies can be found online, and I would recommend it to anyone with a more-than-casual interest in the genus.