There is no doubt that Fallopia japonica - it used to be called polygonum - is a very serious weed. Its elimination can cost hundreds of thousands of pounds on a single building development.
It is not difficult to control in the private garden, but you must not take your eye off the ball and it will take time. If you have the misfortune to possess a strong growing clump it will take at least three years to clear it using herbicides. Without herbicides it will be a complete nightmare, but with much persistence and a great deal of effort you can still achieve complete control.
I do advise that you eliminate this plant. Although it is not unattractive and you might feel it not to be a problem, beware! You might find yourself with some very expensive provisions if it gets into your neighbour’s garden and, should you or your neighbour want to build an extension and planners become involved, well need I say more? It’s best to quietly get rid of it before it ever becomes an issue. Some people are so frightened that it can even affect the value of local property.
It will normally take at least three years to get rid of a strong clump of Japanese knotweed by spraying with glyphosate. It’s worth repeating what I have previously said about a principle that applies when eliminating difficult perennial weed - the actual work involved is quite small, it’s just that it is spread over a long period of time!
In my own case, in Worsbrough cemetery garden, I eliminated a vigorous quarter acre stand of luxuriant ten foot high knotweed, but it took ten years. It took me two years to ‘break the back’ of the problem and I then lost focus. The area just became part of my less frequent and weaker spraying routine.
I propose to describe my own methods and the very exciting recent success of Peter Williams in a garden in Derbyshire.
About Japanese knotweed
Native to Japan, it grows on Mount Fuji above 2400 ft and is an efficient first coloniser of infertile volcanic slopes. It make me wonder how such a vigorous plant obtains its nitrogen. The Japanese call it ‘itadori’ which means ‘healer of the sick’, and I recently read how its shoots can be used to make a very fine gin! So much for hysterical claims from the Ministry that you should wear protective clothing, a mask and generally look like a spaceman and terrify the local population just to burn the tops
It is however a pretty tough cookie. On volcanic slopes it grows close to fuming fumeroles. No wonder it can take over a garden or claim large tracts of riverbank and wet ground in the wild. It has a fantastic ability to smother and kill competing vegetation. This plant really is allelopathic and exudes plant killing toxins.
The problem of Japanese knotweed has become worse where Fallopia japonica has hybridized with other vigorous knotweeds such as the Russian vine, Fallopia baldschuanica. This is rather similar to the problem I wrote about recently with the hybrid Rhododendron x super-ponticum.
Sources as reputable as the Environment Agency will tell you that the weed can spread as much as a meter a month and grow more than 10cm per day. It is surprising how quickly plants grow under optimum conditions. Just google how far common creeping thistle will spread in a season! Yes, Japanese knotweed will spread very quickly in a wet month in August when there is no competition and yes, it will shoot up to ten foot high in very few weeks in June and July. Plants commonly grow rapidly in short vigorous bursts but then stop. Yes, it is a very real problem and has the ability to speedily spread, but I do find the propaganda somewhat overstated.
There is a rumour that it is illegal to plant Japanese knotweed in a garden. I wouldn’t recommend it, and it is definitely illegal to introduce it into the wild. It originally became a problem because it was introduced as a garden plant. A few years ago I visited a botanic garden (not one in God’s county) and admired their magnificent Polygonum japonica (as it was then called). The plant was confined by a lake on one side and a broad band of regularly mown turf on the other. Absolutely superb.
My experience in Worsbrough cemetery.
I explained in an earlier post how nearly twenty years ago, with the help of the naughty boys on probation who were doing community service, I eliminated more than acre of seven foot high brambles in the wooded cemetery. Within the overgrown jungle was an irregular clearing of a quarter of an acre of very well established Japanese knotweed. The colony was bounded by a sturdy cemetery stone wall, trees and brambles. It was virtually impenetrable and grew as strongly as on any riverbank in Wales. I make one visit per month and in the first few years I had other ‘fish to fry’ and completely neglected the knotweed. It remained confined, I did nothing, but it did not spread much further.
Eventually I got round to the fascinating horticultural challenge to kill it. I started on my project at the ideal time in late June when it had achieved maximum height and the leaves were still soft and receptive to my glyphosate. The literature does not confirm my opinion and says that translocation is more effective later in the season. I agree this is true of some translocated herbicides other than glyphosate.
Japanese knotweed has a very limited season, not emerging until after severe Spring frosts and making no further growth after Autumn frost arrives. I would be able to spray about three times a year.
As Is my wont when faced with difficult weeds on the first occasion of spraying I used my glyphosate at the maximum permitted concentration (and a little bit more) and gave them a drink in the morning and for good measure another later in the day. It was not possible on that day to reach all the weeds with my knapsack sprayer, even with its extended lance. I was aided in my efforts that the clump was irregular in shape and I could get in at the edges. I sprayed three times that season. The three sprays took in total, about six man-hours. I did the same in the following year. By the third year strong new growth had ceased and ‘bonsaied’ new growth was only about a foot high. As far as I was concerned, ‘job done’ and the site only received my normal maintenance spray. The knotweed did take another eight years to be completely eliminated but I am certain had I continued with my former intensity it would have been completely killed by the end of the third year.
It is rather ironic that other than Keith Burkinshaw the cemetery sexton, hardly a single Birdwell resident knew that they had a Japanese knotweed problem in their locality. They were certainly unaware that I had solved the problem for them. Nobody noticed! St. Mary’s Church community pay me generous travel expenses for my monthly visit and pay for my glyphosate but the marginal cost to them of eliminating the weed was zero.
In contrast I received an anxious phone call from Bolton Percy church warden that someone had spotted knotweed in the cemetery and there was a bit of a local panic.The cemetery has never seen Japanese knotweed. The plants that had been spotted were completely harmless Polygonum persicaria that I have planted.
Peter Williams’ exciting success in a private garden…. somewhere
Application by injection is not a new principle. It worked very well for Peter this Autumn. The problem was that there were a few very healthy clumps of knotweed in someone’s garden. Some metres away there was to be a new building extension. There was not a cat’s chances in hell of the knotweed harming strong new building foundations. Unfortunately the plants reputation to penetrate badly laid or crumbling tarmac and its acknowledged ability to penetrate cracks made it wise to eliminate it.
This is what he did.
He drilled the base of each tough stem and injected a 10% glyphosate solution. This was at the beginning of September. The quantity of the weed was about twice that in the picture and it took him two hours. I asked him if the method would translate to larger plantations and he said no, it was too labour intensive, he would spray.
One month later the top of the knotweed was dead and he cut it back to the ground. None of the surrounding ornamental plants suffered any damage what-so-ever. For practical purposes the knotweed was gone until next June!
Now the question is will it come back? Almost certainly yes, and the knotweed must be allowed to grow a new top before it is re-treated, perhaps the then much weakened and smaller knotweed will be sprayed.
I have no experience of Peter’s method. Wouldn’t it be wonderful if the Japanese knotweed has been killed outright. I doubt it, but I will keep you informed.
Does digging out roots help?
No digging was done at Worsbrough and I do not imagine Peter intends to dig either. The professional literature suggests that a combination of root removal and spraying is best. This might well be true but it is very important that you spray the undamaged intact weed first.
Further technical and legal information provided by Peter Williams and quoted verbatim
Looks an interesting article and I assume you have some pictures of the foliage to show just what a beautiful plant it is. You might refer at slightly greater length to the timing of spraying or injection - The sources I looked up all stressed the need to spray late in the growing cycle when nutrients were being translocated back to the roots for overwinter storage. I used just a few ml of glyphosate per shoot and as you say nothing in the area was affected even the grass growing very near the clumps.
Its distribution is also possibly worth a mention - whereas it is very widespread throughout Britain (as shown by the national 10x10km grid square data) it is only locally very common and usually in past industrial sites ( as shown by reduced presence in 2x2 km squares).
Interestingly Edward Salisbury in the classic work on weeds in 1964 (2nd Ed) hardly mentions this plant but he does quote the RHS journal ‘The Garden’ for 1897 thus "A plant of sterling merit, now becoming quite common...and is undoubtedly one of the finest herbaceous plants in cultivation". He goes on to comment that that reputations can be lost and it can be seen on waste ground in London and once established "it is a labour to eliminate".
It might also be worth mentioning the Cornwall County Council website that is helpful without being over dramatic and does I think, cover all the legal issues.
Japanese knotweed (fallopia)
Not just a weed but a biohazard. Introduced from Japan mid C19. In
Japan it does not cause problems because of its natural pests and
predators. These were not introduced with the plant into the UK.
Noted in wild in London 1900, Exeter 1908 and Suffolk 1924. Cornwall
1930. By 1960’s Land's End to John o Groats and beyond to the isles (isle
of Lewis?). Although it flowers, spread is vegetative - roots
extend 2 m down and 6m laterally per year. (p263). Spreads in urban
areas/churchyards but not in ancient woodlands or grassland or
agricultural land. Japanese knotweed is listed on Schedule 9, Part II
of the Wildlife and Countryside Act 1981 making it an offence under
Section 14 (2) (a) of the Act to "plant or otherwise cause Japanese
knotweed to grow in the wild". Both the Police and local authorities
have enforcement functions under the Act. Penalties for a Section 14
offence have been modified by the Countryside and Rights of Way Act
2000 for England and Wales. A magistrates’ court can impose a maximum
fine of £5000 or a maximum prison sentence of six months, or both. A
Crown Court can impose an unlimited fine or a maximum prison sentence
of two years, or both.
Under the Environmental Protection Act 1990 above and below ground
parts were classified as 'controlled waste' and have to be disposed of
in licensed landfill sites only. The fear and legislation relating
to this species led to the establishment of a specialist industry
aimed at its destruction. The industry stressed the dangers of the
plant and pointed out the difficulties not only of killing the weed
but also its subsequent disposal. Public authorities and worried
private citizens employed the contractors and business boomed. This
developing 'pest removal' industry received another boost in 2009 when
the Finance Bill allowed companies tax relief of 150% on the cost of
removing knotweed from contaminated land. The price for clearing the
weed rose to above £50 per square metre and the annual cost in GB in
2010 was in excess of £150 million. Clearing the Olympic site cost
Thank you Peter You have given much food for thought.