Knotweed noshing

Of all the early spring plants that I forage, nothing smacks me in the taste buds quite like Japanese knotweed. It has a sour, tart taste like rhubarb, and it’s a delightful change of flavour after a winter of root and frozen vegetables.

If you haven’t heard of Japanese knotweed, chances are you have seen it. At maturity, in late summer and early fall, it has large, broad green leaves with small clusters of flowers on a long stem. The stalks are hollow, like bamboo, with regularly spaced nodes.

L: Mature stand. M: Flower R: Dead stalks.

It’s reasonably attractive, but it’s an invasive plant that can grow up to 4-5 m tall (~15’) and take over large pieces of land in record time. This is definitely not one of those plants you want to bring into your garden unless you enjoy having your neighbours say nasty things behind your back.

Japanese knotweed reproduces primarily through rhizomes in the roots, which spread horizontally underground, but it is also spread by seed in late summer. It’s one tough bugger; it can grow in as little as one gram of soil, or from as deep as one metre.

Lots of people just want it gone and will go to great lengths to kill it—using chemical and non-chemical means—and I understand that urge. Years ago, I had some in my backyard that just kept coming and coming. After three years of smothering it with bags of yard waste, black plastic, and old bits of carpet, I finally got it all, which is kind of a pity, because I learned too late that I could have been eating it.

If you harvest Japanese knotweed stalks at the right time in the spring, you can curtail its spread underground, plus stop them from growing up to flower and seed.

Finding it

NOTE: Japanese knotweed can grow in polluted soil just as well as does in clean soil, so find out as much as you can about the area that you’re harvesting from. If in doubt, don’t put it in your mouth!

Here in Ottawa, Japanese knotweed typically arrives in late April or early May, depending on local conditions. Look for the tall, brown stalks of last year’s plants; the new nubs will be beside them, usually under leaf litter, and are bright red. Once you find the nubs, it’ll only be about a week before they turn into green and reddish stalks, with the hallmark nodes, and a leafy top.

L: Ma Nature has no problem showing off her knotweed nipples. R: Stalks are ready for harvest when they reach about 6″ high and resemble asparagus spears.


Harvest the stalks when they’re 15-20 cm (6-8”) tall and are more green than red. Once the stalks go over about the 20 cm mark, they become woody and thick, and lose some of their flavour.

Cut the stalk about 1 cm (¼-½”) from the base with a sharp knife or scissors. Use paper bags, a box or basket to transport them; moisture will build up in a plastic bag and turn them mushy.


Cut off the leafy top then give the stalks a rinse with cold water, making sure that the water runs through the hollow stalks. Don’t soak them or they can turn mushy.

When young, the outer layer of the stalk is quite thin. I’ve peeled it off in the past but that can be a fiddly process, so now I leave the peel on. I use knotweed primarily in cooked dishes, so, like many other fruits, the skin will simply cook down. If you choose to peel it, the quickest way is to use your fingers, but a small knife works, too.

Nutritional value

Japanese knotweed is a perennial herb and is a source of Vitamins A and C, iodine and the antioxidant, resveratrol.

Ideas for use


Cut up chunks and add to cakes, muffins, or pair with other fruits in pies or tarts. Could also be used as the filling for layered cakes, crepes, or sweet doughs (knotweed buns anyone?). I’m going to give knotweed cheesecake a try this year, possibly pairing it with those lychee fruits I’ve had in a can in my pantry for the last six months.

Knotty Sauce

Cut the knotweed into chunks, put them into a pot, and bring the mix very slowly to a boil. Do it slowly to give the knotweed time to start breaking down and releasing juice. If you throw a little salt on it, it’ll help draw the water out and you may not need to add any more water. If, however, it’s looking too thick, add a small amount until it reaches the consistency you want. Once it’s boiling (it actually looks more like a burping lake of prehistoric ooze), take it off the heat and put a lid on it. Once it’s cooled, mash it by hand or in a blender. Freeze in ¼ or ½ cup sizes for baking, or in ice cube trays to add to smoothies, pesto, or sauces.


Adds an interesting dimension to pesto—the regular, basil kind of pesto, or any pesto you may make with wild or domestic greens.

Add some chopped up knotweed to your next soup or stir fry for a sour hit. I find it goes best with clear soups (vegetable/chicken stocks) or cream soups (e.g., mushrooms, potato).

However you end up using Japanese knotweed, I’m always interested in learning how people are using it so please share your recipes and ideas with me.

If you plan to start foraging, do your research. It is your responsibility to correctly identify plants for consumption. Anyone can have an allergic reaction to any plant, so do your due diligence. If in doubt, don’t put it in your mouth!

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