Japanese knotweed – Identification, distribution, edibility

Fallopia japonica (UK) or Polygonum cuspidatum (US)

Japanese knotweed shoots at their prime edible stage

Japanese knotweed shoots at their prime edible stage

  • 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!
Japanese knotweed

Japanese knotweed – by this stage its stems have lost succulence and become too fibrous to be worth processing

“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). 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.

The Triffid Sour – Gin, sweet cicely syrup, clarified Japanese Knotweed juice

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.

Making japanese knotweed and sweet cicely vodka. These 2 ingredients combine exceptionally well - try them in ice cream, jams, fools, cumbles too

Making japanese knotweed and sweet cicely vodka. These 2 ingredients combine exceptionally well – try them in ice cream, jams, fools, cumbles too

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.
These died cut stems of japanese knotweed have been died to show they have been injected with poison. This is not universally practiced, so absence of dying should not be taken as a sign of an untreated site

These cut stems of japanese knotweed have been died to show they have been injected with poison. This is not universally practiced, so absence of dying should not be taken as a sign of an untreated site

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.

A super-delicious dessert by chef Craig Grozier: Japanese knotweed, buttermilk, magnolia, sorrel

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.
Japanese knotweed - an attractive plant?

Japanese knotweed – an attractive plant?

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.

knotweed root capsules

Knotweed root tablets, sold as  a medicine in Japan. These were being marketed to combat symptoms of Lyme’s disease

japanese-knotweed sale

Somebody making some easy money selling japanese knotweed on a market stall. Such practices should be accompanied by clear information about safe handling and disposal of trimmings

s mackerel, knotweed puree, pennycress

Smoked mackerel, knotweed puree, pennycress salad

Japanese knotweed and sweet cicely compote with greek yogurt.

Japanese knotweed and sweet cicely compote with greek yogurt.

Guinea fowl with steamed sea kale and knotweed sauce

Guinea fowl with steamed sea kale and knotweed sauce

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!
Related pages:

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12 Comments

  • IWA says:

    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.

    • mark says:

      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.

  • Bonita Smith says:

    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?
    Thanks

  • Barry says:

    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.

    • mark says:

      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

  • Susan says:

    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 .

    • mark says:

      Hi Susan,

      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!

      Mark.

  • Elaine says:

    Hi
    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?
    Thanks
    Elaine

  • AMANDA CREE says:

    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?

    • Mark Williams says:

      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!

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