Drinks uses of Japanese Knotweed


Mention japanese knotweed (Fallopia japonica in the UK or Polygonum cuspidatum in the US) to most people and they are quite likely to shudder, pull a face, and tell you what an awful plant it is.

Likewise, if you search for it online, you will have to sift through 100’s of listings dramatically decrying it as a “monster plant” before you find a single one that says anything positive about it. This is kind of understandable. It can be a nuisance and you really don’t want it in your garden – it can rapidly dominate and its very presence could easily half the value of your property. But the villification has got a little out of hand in my opinion. Fearmongering is spurred on by a multi-million dollar chemical eradication industry that pumps untold gallons of herbicide into the ground each year, but, I rather suspect, doesn’t want to be so successful that it goes out of business…

With this in mind, i’d like to paint a rather more balanced picture of this remarkable plant, which offers some great possibilities for switched on foraging bartenders and tipsy botanists at home. I believe there is a great opportunity to spread some very positive messages about how we might control this “monster” without resorting to chemicals.

Very Important Harvesting Considerations:

  • Japanese knotweed is seriously invasive and can reproduce and infest new areas from tiny fragments. It establishes itself very 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 you intend to remove on the already infected site. You don’t want to be disposing of any in your compost – it will overrun your garden in no time, and it is an offence to “cause it to be in another location”. Any and all JK removed from a site must be pulped, burned or cooked before disposal.
  • Many patches of knotweed in public places and gardens will have been treated with poison. 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 a while. Any cutting back is usually accompanied by chemical treatment. Whatever poison is used is likely to have wreaked havoc with surrounding vegetation too. Often (but not always), poisoned stumps are died blue or green. Local authorities should be able to tell you which areas have been treated. I tend to harvest mine from a large patch on an isolated bit of coast that isn’t upsetting anybody.

JK is in the scientific family polygonaceae along with rhubarb and sorrel.

JK is in the scientific family polygonaceae along with rhubarb and sorrel. Its not surprising then, that they share many characteristics, notably rapid growth, juicy succulence and a sour flavour. The flavour of all three comes predominantly from oxalic acid, a mouth-watering (literally and metaphorically) compound that comes with some health warnings: anyone with kidney problems, or who has been advised by their doctor to avoid spinach or rhubarb should restrict their consumption. Please don’t let that put you off: there are very few things that aren’t bad for you in the wrong dosage! Rhubarb and sorrel contain similar concentrations and are widely used. I should also say that JK has lots of good things in it too, and is revered in some eastern cultures for its anti-ageing and anti-carcenogenic properties.

You can find JK in many habitats, notably by the coast, unloved gardens, wood edges and especially urban riverbanks.

The ideal time to harvest is when the young shoots are between 10 and 60cm, with limited formation of leaves (see pictures above). In the UK this usually occurs over a 2 month window between mid March and mid May. Prime shoots should be stocky, like fat red and green aspragus, breaking with a pleasing hollow “snap”.

The flavour of JK is somewhere between rhubarb and gooseberries and I have explored the following ways of extracting flavour for drinks:

The flavour of JK is somewhere between rhubarb and gooseberries and I have explored the following ways of extracting flavour for drinks:

Raw juice: Either in a hand-cranked “wheatgrass” juicer or in a rotary juicer. The resulting liquid comes out thick and green. It can be used this way (think of it like orange juice “with bits”), but makes for a pretty murky green drink! Passing through muslin has limited effect, but if you leave it in the fridge for 12 hours, the green pulp sinks and you can skim off a beautiful, clear pink juice from the top that makes an excellent light, fresh, crisp acidifier. A commercial centrifuge would work well here.

Cooked Juice: Chop the stems and simmer lightly with a little water for 15 minutes before blitzing and passing through muslin. The resulting liquid looks green initially, but soon turns a pleasing purple colour throughout. Not so light as the raw pink juice, but still an excellent sour mixer.

Infusion in Alcohol: 2/3rds fill a kilner with chopped raw JK then top up with vodka (min 40% ABV). This improves with age, being worthwhile after about 1 month – or try rapid infusion. Sweeten to taste.

Wine: I haven’t made wine with JK or tasted it, but those I know that have rate it highly.

Thoughts on pairings: JK goes extremely well with sweet aromatic flavours. My favourite accompaniement is sweet cicely, whose sweet aniseed and deeper notes work exceptionally well with the sour fruitiness of JK. Vanilla/courmarin flavours such as meadowsweet, sweet woodruff and elderflower also work extremely well. Try adding some to an infusion.

JK straws: The hollow shoots of JK lend themselves very well to use as natural straws that enhance the flavour of the drink. Select one of appropriate length and push a skewer or chopstick up through it, piercing the membranes between segments.  Either chop off the tip, or insert a short straw in the top.

I hope this article will inspire some thoughtful experimentation with this remarkable plant. I think it is possible for mindful bartenders and small businesses to generate some very positive stories around japanese knotweed, spreading messages of mindful control, responsible foraging and the gastronomy of “weeds”. But this could all be rubbed out by one incidence of careless disposal – so please be careful!

Japanese Knotweed syrup recipe


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