Japanese knotweed – Identification, distribution, edibility
Reynoutria japonica (previously Fallopia japonica (UK) or Polygonum cuspidatum (US))
- Edibility – 4/5 – Young shoots and tops cooked/eaten like asparagus, stewed like rhubarb or juiced. See important notes on harvesting below.
- Identification – 5/5 – Green/red speckled hollow stems and bright green oval leaves growing in thickets
- Distribution – 4/5 – Abundant throughout the UK
- Season – March – June for young shoots
- Habitat – Waste ground, roadsides, coast, old gardens and especially riverbanks – anywhere really!
“Weed” (n): Any plant that has mastered every aspect of survival except growing in neat rows.
This invasive species is widely despised for its virility and tenacity and general success in the west, but the Japanese revere it as Itadori – which means “tiger stick” (on account of its brightly striped canes), though I have also seen this translated as “strong one”. This may be to do with its ability to grow nearly anywhere and force its way through pavements, but more likely for its wide range of health-giving properties (it is also being clinically trialled just now in the treatment of Lyme’s disease, and is recommended by Stephen Buhner in the herbal treatment of flu viruses). Better still, it is delicious, with a taste somewhere between gooseberry and rhubarb. Young shoots are great stewed down with a little sugar and water, passed through a fine sieve and served with greek yogurt or as a fool. It can be used in savoury sauces too, to cut through oily fish or rich game. It works well in fruit leathers too – see here for how to go about making them. It also makes a wicked flavouring for vodka, especially paired with sweet cicely. See this page for how to make the schnapps. I have written more extensively on the drinks uses of japanese knotweed here.
Japanese knotweed is high in oxalic acid, so you should eat it sparingly if you have kidney a complaint or have been advised to avoid spinach or rhubarb. On the plus side it is a rich source of resveratol and vitamin C.
The young (and rapidly growing) shoots are best harvested when they are less than 50cm long. The younger you harvest them, the less fibrous outer you will have to peel, and the more juicy inner you will have, if you wish to cook it like rhubarb. Personally, I find peeling too much of a faff (especially considering the need to cook or burn all trimmings), so I tend to chop and cook the whole lot, then pass through a sieve to make a purée.
Another way to go is to juice whole raw stems. This results in eviscerated pulp which can be composted, and gloopy green juice which can be drunk in smoothies, or passed through a fine cloth to make a beautiful, clear purple juice. An excellent mixer in a gin cocktail!
IMPORTANT HARVESTING NOTES:
- Japanese knotweed is seriously invasive and has the ability to colonise new areas from small fragments. It establishes itself quickly, and its rhizomes can go 3 metres deep and stretch up to 7 metres from the plant. Be sure to fully trim all shoots on the already infected site. You don’t want to be disposing of any in your compost – it could overrun your garden in no time. Neither should you put any trimmings in a bin that will end up in landfill. Cooking or burning of all you bring home is essential.
- Before you even consider harvesting japanese knotweed from the wild, you should seriously consider your social, environmental and legal responsibilities with regard to the safe disposal of the the parts you don’t eat. Section 14 of the Wildlife and Countryside Act 1981 states that “It is an offence to: … plant or otherwise cause to grow any plant in the wild outwith its native range”. Putting aside some righteous incredulity at this (I rather think the Forestry Commission would go bust if they got a bill for the millions of sitka spruce they’ve planted), you should take this seriously.
- Legally (in accordance with UK government advice), if you have JK on your own land, “you must prevent [it] from spreading into the wild and causing a nuisance. You could be fined up to £5,000 or be sent to prison for up to 2 years if you allow contaminated soil or plant material from any waste you transfer to spread into the wild“.
- Many patches of knotweed in public places and gardens will have been treated with herbicide. As even untreated patches die back fully over winter, and poisoned ones may continue to grow new shoots after years of treatment, it isn’t always easy to tell which are safe to harvest from. It is best to keep an eye on potential patches for at least a year before considering it as food. Any cutting back by councils/land managers is usually accompanied by chemical treatment, which results in rapid die-back of growing parts (a withered, burned look). The only herbicide licensed for use near water courses, where the majority of (but by no means all) JK is found, is Glyphosphate. This requires licensing from the Scottish Environmental Protection Agency (or the Environment Agency in England). They should be able to tell you if an area has been treated, but good luck with that. While the UK government publishes information on pesticide residue in food, it has a somewhat narrow view of what it considers to be food – and no interest in wild food.
As with many “invasive species” (american signal crayfish and himalayan balsam spring to mind), knotweed gets an awful press – in my opinion some way beyond the actual problems it causes. Never forget that a multi-million pound industry has sprung up around controlling it. This industry has financial reasons for vilifying it and no reason to get rid of it completely. I have met well-meaning people – often working in environmental protection organisations – that are so rabidly fixated on its control/destruction that they appear to have lost all sense of perspective.
Don’t misunderstand me: I have every sympathy for people struggling to rid it from their gardens, and it certainly requires some control in public areas. But people obsessed with waging chemical warfare on it tend to forget the following:
- It is an attractive plant if viewed through unprejudiced eyes – its huge whorls of tiny delicate cream flowers look stunning in late summer and turn an attractive rust colour in autumn. Lest we forget, it was first introduced by the victorians as an ornamental plant.
- It provides an excellent habitat for birds, small mammals and lizards (including some rare species).
- Er…what about the thousands of other introduced species that are doing rather well? For example, sitka spruce renders probably a million times more land impenetrable and ecologically sterile. People got tax breaks for planting that, and public bodies like the Forestry Commission still replant 1000’s of hectares a year, though they do have more enlightened planting policies nowadays.
- This battle is un-winable. Almost all public control campaigns focus on sloshing millions of gallons of glyphosphate into the environment – which is frankly scandalous: Is glyphosphate going to be the next major health scandal?
- All plants are “invasive” given the chance!
- Just to repeat…it is edible, delicious and extremely good for you.
Most foragers are, by nature, pragmatists. Why not make the best of a bad job here and educate people on harvesting and control? Keeping people in fear and ignorance by inventing the “monster plant” myth doesn’t strike me as a very thoughtful or progressive way forward. For inspiration on an alternative approach, check out this scheme where knotweed is controlled naturally by harvesting 7kg per square metre, making some good money from it, then re-naturing the site with less offensive species. I am currently working with a wide range of chefs, brewers, distillers and educators to find thoughtful, responsible ways to use japanese knotweed. Please don’t hesitate to get in touch if you’d like to explore possibilities.
Rant over. Here are some more pictures of this remarkable plant.
Incidentally, I have a foraging friend in the south of England who likes the flavour of japanese knotweed but couldn’t find any unpolluted locations near him. So he planted some in his garden. He couldn’t get it to grow!
I’m mentioning this purely because I find it funny. His actions may be illegal and possibly irresponsible and i’m really not suggesting anyone emulate this act!
- wild plant guide
- Sweet cicely – edibility, identification, distribution
- Foraged cocktail – Islay Spring – including how to make japanese knotweed vodka
- Wild food recipes
- wild foods in season now
- Edible invasive species guide
- Drinks Uses of Japanese Knotweed
Looks like one of your images has been stolen and used without your consent by a firm called War on Weeds. Google it and you’ll see. They nicked pretty much every image on their site.
Thanks, but TBH, it wasn’t my image in the first place! Nearly all the images on this site are mine, but I “borrowed” a lot for this page.
I Have lots of it and have it since I have lived here- 9 yrs. It is a privacy screen and I have dug some up to make privacy in the back yard. I have found it easy to handle. I just pull out the little ones that go beyond their line!
Can I really eat it?
Yes. As mentioned in the article.
I still have nightmares about this stuff, I couldn’t bring myself to try it no matter how great it tasted. I’m glad someone is making good of it’s existence, but please heed the warnings about handling this plant and avoid taking any away from infested sites. It’s nasty nasty stuff that can turn into a forest in a matter of weeks and month. I spent 4 years treating this stuff unsuccessfully from an old house, an ordeal I would not wish on my worst enemy.
Hi Barry, Sorry to hear you had such problems. Extremely careful handling of waste is the crucial other part to the “eat to control” message and I hope it comes across clearly here. In some situations, a change of perspective can help alleviate the “nightmare” feelings. Check out this guy who eradicates it without chemicals and makes £70 per square metre out of it: http://www.newtritionink.de/shop/pdf/english.pdf
Thank you for this info! I have been looking into using this for Lyme treatment and I am moving some out of a freinds road side to my property so we can enjoy wild grown food . I can’t wait for it to grow! I will transplant it at the edge of the tree line 500 feet from my house and figure I can control it by mowing . What do you recommend as a good planting area to contain it well .
I wouldn’t – in any way – recommend planting JK or encouraging it. Doing this is illegal in the UK. Mowing might keep it under control, but what if you move away, or for any reason can’t mow it? My advice is on better use of a problem invasive where it already exists – not intended to encourage its spreading!
Do you have enough to supply me with some, as I would love to source it from the wild to use rather from unknown sources as I do at present?
I don’t supply any wild food, only teach people to gather their own.
Thanks for your rational environmentally kindly writing on this plant. i love the sculptural quality of the leaves but i find the flowers attract clouds of flies of the bluebottle type rather than bees. Any comment?
Thanks Amanda. Bees and butterflies (rightly) get lots of press for their importance and industrial persecution, but most people overlook the ecological importance of flies, moths and other insects in pollination roles. Another case of prejudice I fear!
I am an environmentalist and have been controlling this stuff and my star plant that of ponticum for decades. But with age comes wisdom (sometimes) there is a problem when it goes near a fragile ecosystems where its vigour can destroy. The problem is us and not it. But i have come over to the eating side! Thanks for the article. Looking forward to spring with new eyes! Keith
RE: susan, transplanting and mowing.
im from washington state in the US so i have no experience with UK law, but as mark said there are legalities to consider, and future problems that are easy to overlook. my reason for commenting is specifically mowing. i would advise 10000 times to not mow or attempt to control this plant by any means that spread any part whatsoever no matter how small. best to harvest and burn waste. my grandparents had a very small patch show up on their 1 acre property one year. i was a wee child around 8 or 9 and she figured since i lived there and being a rambunctious young boy she would assign me the mission of heading off the invasion. always armed with sticks of a wide array of calibre, and access to the more combat ready machete she tasked me to confront and destroy any of them i see. after two months the small band of my enemies had grown exponentially. i was hemmed in on all sides desparately fighting the invading force in a deep dense jungle comprised of the enemy themselves! i could do nothing to gain the upper hand or even keep pace with their spread. i could get lost in there for hours. i found myself in heated battle just cutting trails and clearings inside the quagmire. every little piece sprouted new plants. over a couple months i singlehandedly caused a patch of 5×7 or so, several plants is all, to cover nearly half the acre they owned. it took almost a decade of yearly cutting of every single shoot that came up below the lowest node placing them on sheets of plastic and introducing round up into the stalks, and burning the whole mess including plastic to ensure no pieces were left. and to maintain for that growing season doing the same to any shoots as they rose after the initial process. i learned later, onlu very recently, of its value as a foodsource, and i found a few in a shady area in my lawn. i cut them and eat them as i see them get big enough and put a couple in a large pot on a piece of sheet metal as a plate to keep the roots contained (also how i contain my mint). the potted ones have yet to spread as i cut long before they seed and the roots are contained. being in shade also slows growth and spread. the ones in the yard still have grown only a few stalks in almost 4 years. but every time i mow i go ahead and cut any i see growing there first. i first found two.. today there are i think six when they shoot up. sorry for the epic story. the imagery is not exaggertated lol. they spread and grow so fast. in my experience, if in sun and allowed to grow without strict careful control, and with shredding and dispersal of any part of the plant, they will outpace hialayan blackberry without looking back. they are quite palatable tho. thank you and good luck.
i recognize this is 4 years too late lol, if you have already decided one way or another maybe this will reach anyone else thinking of the same..
I am very much interested in Japanese Knotweed and it’s medicinal uses. I am a amature Forager I also have
atherosclerosis and high blood pressure. I’m already aware of some of the benefits of the Hawthorne Berry and leaf for such conditions. I put little faith in our government re medication and being healthy and longevity.
Many thanks in advance
Magnificent web site. Lots of helpful information here.
I’m sending it to several pals ans additionally sharing in delicious.
And obviously, thanks on your sweat!