There are plenty of choices for plants that are a nuisance and almost as many for those that are a damned nuisance or worse. Depending on your location and circumstances it could Brambles, Nettles, Docks, Ground Elder, Marestail, Hogweed …the list is almost endless. But to name a plant that can stop you getting your house insured or that is powerful enough to break through tarmac or concrete doesn’t leave you much choice. It has to be Japanese Knotweed.
But you can see why Knotweed – botanically Fallopia japonica – was a smash hit with gardeners when it was first introduced in the 19thc. It is an imposing plant, with sprays of beautiful white flowers, strong architectural form and lush foliage. Of course what they didn’t know initially, although it didn’t take that long to find out the hard way, is that is rampantly invasive and virtually impossible to eradicate. It’s no wonder its been declared a public nuisance and was proscribed from being planted in 1981. Yet I’ve seen the same plant growing under controlled circumstances in historic gardens so just maybe, potentially, perhaps, it is remotely possible to have the best of both worlds.
Taxonomy as always is convoluted and complex. It’s not just that names change but also because the various members of the knotweed tribe hybridize with each other and then incestuously backcross with their own parents. There is a link to further reading at the end should you wish to tax your brain further with this. What follows is my [limited]understanding of the situation
There is no evidence of live Japanese knotweed in Europe before the 19thc. However it did arrive, presumably as a dried herbarium specimen, from Japan in the late 18thc when it it was officially described as Reynoutria japonica by the Dutch naturalist Maarten Houttuyn. This was in Natuurlijke Historiae in 1777, a compendious 37 volume collection of matters of botanic and other scientific interest, which might have made him famous except it was all in Dutch. But it did have an illustration. Unfortunately Houttuyn described it slightly mistakenly so that it was not recognized by the great Swedish botanist Pehr Thunberg, who had actually been to Japan, when he wrote his Flora japonica. Instead Thunberg introduced and described another member of the family, Polygonum multiflorum [now Fallopia multiflorum].There is an argument about who introduced the first live specimen to Europe – perhaps not an argument you’d want to win. Knotweed was certainly in a large collection of plants which came back with Philippe von Siebold in 1830 after his 8 years in Japan. In 1841 he opened a nursery and ‘garden of acclimatization’ in Leiden where he propagated and then distributed plants from his collection both commercially and to botanic gardens.
He named knotweed in 1845 as Polygonum cuspidatum and in 1847 it won a gold medal for being the best ornamental introduction of the year. In his nursery list of 1848 it was listed as Polygonum sieboldii and cost 500 francs – might not sound much but that was same cost as it was to buy 500 wisteria sinensis from the same list, which gives some indication of its rarity and supposed value.
In his 1856 catalogue Siebold described its properties and benefits, and it was clear he thought it had economic as well as ornamental potential. Bees loved it because it was full of nectar, livestock loved it for its nutritious foliage, its flowers were good for floristry, its root system stabilized sand dunes and unstable ground, it had medicinal possibilities, and you could even make matchsticks from the dried and split stem. What’s not to like!
But there were earlier rival claimants in London. Joseph Paxton and John Lindley claimed that knotweed had been growing in the bog garden at the Horticultural Society’s garden in Chiswick as early as 1825. However they was thought it was Chinese in origin and probably Houttuynia cordata– by coincidence a species named after Houttuyn. This is now a common ornamental waterside plant, and its young shoots do indeed resemble knotweed. The specimen failed to thrive at Chiswick and only flowered once in 20 years.
Nowadays it’s accepted that this was first live Fallopia japonica in Europe, although no-one knows how it got to Chiswick, but analysis of the surviving drawings apparently suggest it was a Chinese strain. Given its poor performance, its unlikely it was ever propagated or distributed, so it really is Siebold who is responsible for the nuisance we all know and love.
To confuse matters a little further Kew’s herbarium contains a specimen of what was then classed as Reynoutia multiflora sent back from China by Robert Fortune in 1845 but a live plant only arrived at Kew in August 1850 in a large consignment of plants sent by none other than Siebold. It was part of his plan to exchange ‘novelties’ from China and Japan with botanic gardens across Europe. Kew has a herbarium specimen of this dating from 1857, but although its Out Book records huge numbers of plants being distributed there is no mention of anything that might be the knotweed before 1856.
And to add more confusion, a plant named Polygonum seiboldii reached the Royal Botanic Gardens in Edinburgh in 1854 but not from Seibold. Instead it came from the Kingston nursery firm of Jacksons – just down the road from Kew. It is not known where Jacksons obtained it, but the spread was clearly already underway, albeit slowly.
Siebold’s 1844 catalogue also records a dwarf knotweed and that was later recommended by Gertrude Jekyll in some of her planting schemes including Long Aston in Birmingham [Richard Bisgrove, The Gardens of Gertrude Jekyll, 1992]. Other herbarium specimens record this growing at Kirkstall Abbey, Leeds in 1881 and Dunham Massey in Cheshire in 1883. There is also an ‘alpine’ knotweed, just 10cm, high (from high on Mount Fuji ) which has also been recorded at various sites including Myddleton House, the garden of E.A.Bowles. Of course with the opening up of Japan to westerners there could easily have been multiple introductions by multiple collectors.Another species of knotweed, Fallopia sachalinensis, which has much larger foliage, was found by Russian collectors in the mid-19thc and quickly found its way to Kew. By 1869 was being offered for sale as “perfectly hardy”by William Bull’s nursery in Chelsea. It was often chosen as a forage crop or planted for cover on shooting estates where it can still be found.
So now we have two distinct species in Britain – F.japonica and F. sachalinense– but what no-one realised was that they can easily hybridize to become what is now known as Fallopia x bohemica. It must have happened very quickly as there are herbarium specimens collected in the 1870s. What’s worse is that F x bohemica is even harder to control than either of its parents. A supposedly “new mammoth species” growing up 16ft tall, and with each culm being 5 inches round, was also being offered for sale by 1901 by Gauntletts of Redruth who specialised in Japanese plants and which had been sourced in the garden of Henry Cook at Priors Mesne near Lydney in Gloucestershire.
Unfortunately nursery catalogues, especially from smaller regional businesses, are so ephemeral that very few early ones survive. However, John Bailey and Ann Conolly of Leicester University have compiled a table of those they have found which were offering knotweed, albeit under varying and sometimes imaginative or incorrect names. The invasion had begun.
But why were nurserymen offering it so enthusiastically? Why was there such passion for knotweed in the later 19thc? Perhaps one culprit is William Robinson who advocated in The Wild Garden that our native for a should be supplemented and “made beautiful by the naturalisation of hardy exotic species.” And guess what two of his suggestions were? You guessed right I’m sure.
Both Polygonum sieboldii and p. cuspidatum were recommended as”very precious for our purpose”. They were both “plants with large or graceful foliage suitable for naturalization” and “can certainly take care of themselves.” Robinson soon realised the dangers and warned [in the 1894 edition] “they are among the plants that cannot be put in the garden without the fear of them overrunning other things.” But it was too late by then!
Gertrude Jekyll has her part of the blame too. In Home and Garden in 1900 she writes of plants that will create a big effect in very little time in a chapter aimed at gardeners who have short tenancies. After talking of annuals and pots of geraniums she says “we ought not to forget the quick-growing ways of the great Japan knotweed, growing fast and tall.” Certainly any sensible landlord nowadays would make sure it was indeed a very short tenancy!
But Gertrude was not the only one. Her friend and near neighbour Mrs Earle praises P.cuspidata in her Pot-Pourri from a Surrey Garden as “her favourite” and “the handsomest easiest grown, hardiest,most useful plant for London gardens”. It was, she wrote, “a joy from the first starting of its marvellous quick spring growth to its flowering time, and to the day when its yellow autumn leaves leave the bare red-brown branches standing alone afer the first frosts.” Both P.cuspidatum and P sacchalienses required no care apart from making sure “the outside suckers are pulled up every spring.” But she too had recognized its faults because without that “the plant is a useless weed.”
Other great gardeners were equally smitten by the charms of knotweed included Canon Ellacombe, E.A. Bowles, Ellen Willmott and Charles Wolley-Dod, who wrote about it and exchanged plants amongst themselves, even buying more from abroad from Siebold’s successor. It still grows at Bowle’s home, Myddleton House nr Enfield, although well contained and as an educational display.
Its poetic justice that after Seibold’s death in 1866 his nursery was soon abandoned, and when it was visited by nurserymen Peter Barr & F.W. Burbidge in 1883 they found the site derelict and surprise surprise overrun by nothing other than Japanese knotweed.
Ann Conolly mapped its historical spread throughout the British Isles. The first recorded “escape” was in South Wales in 1886 but Fallopia japonica is now so widespread as to be untrackable. The other 2 larger species, F. sacchalienses and the cross Fx bohemica are more restricted in distribution. However the largest stands k of F x bohemica are in west Surrey often near those of F. sacchalienses. And which gardeners who recommended it as a garden plant lived in West Surrey?
To make matters worse in 1906 Gauntletts nursery moved from Redruth to Chiddingfold in, where else but, west Surrey just a few miles from both Miss Jekyll and Mrs Earle. Bailey and Conolly also spotted a similar pattern around former nurseries or landed estates, although on a smaller scale in W Cornwall and S. Wales. [including Trewidden, Lanarth, Clyne Castle, Tredegar, Cyfartha Castle, Gabalfa and Velindre]
There is more bad news. The Siebold introduction was a male-sterile (functionally female) plant and so obviously could not produce fertile seeds. However like all plants knotweed has an inbuilt propensity to reproduce and the consequence has been not only spreading by means of its rhizomes, but also by hybridizing with any remotely similar species.
I’ve already mentioned x bohemica but in Wales in 1983 it also managed to hybridize with Russian Vine, [Fallopia baldschuanica] and similar crosses have since been found all over Europe. Luckily the world has been spared a double nightmare because the resultant cross is a normally a weak curiosity. It was named Fallopia x conollyana – in honour [!] of Dr Conolly’s work on knotweeds. For more about it see John Bailey, The Railway-yard Knotweed. Watsonia (2001) 23:539-541.
UPDATE Jan 2020: MORE BAD NEWS. The RHS magazine, The Garden for January 2020 carries news that F x conollyana HAS set seed although [good news] it has not survived our recent very wet winters. Howver Sophie Hocking, the PhD student leading the resaerch at Swansea University, believes it is posible that by back-crossing with F x japonica it is perfectly possible that it will be able to do so.
This all just highlights the problems of alien species with no known predators or diseases. In Japan, of course knotweed simply isn’t a problem because it’s just one of a number of equally rampant community of plants such as wisteria and miscanthus which share the same habitat and creatures that eat them, as well as pathogens and fungi that weaken them so restricting their ability to take over the world. Some of these natural restraints are being investigated for careful introduction here but don’t hold your breath that they’ll arrive any time soon.
The source for much of the information for this post has been the collective work of the Department of Genetics and Genome Biology at Leicester University, particularly that of Dr John Bailey, their principal experimental officer who has spent much of his working life investigating knotweed in all its shapes and forms. His webpages have a comprehensive list of further reading if you want to pursue knotweed any further.