How to Prepare and Cook Japanese Knotweed

Fallopia japonica is on many state noxious weeds lists. Its relentlessly dense colonies exclude native plants, and it alters local ecologies, choking streamsides and riverbanks. Its shoots can even crack asphalt and concrete.

The choice edible part of Japanese knotweed is its young shoot, which resembles an asparagus spear. These tart stems are stuffed with resveratrol, the antioxidant polyphenol touted for its anti-inflammatory effect. The stockiest, plumpest shoots are the most tender and juicy. Skinny ones tend to be fibrous.

Japanese knotweed has an earthily sour flavor. Mature shoots tend to be more acidic. Raw knotweed is less astringent than the rhubarb to which it’s often compared, but it does collapse like rhubarb when exposed to heat. Moist heat makes knotweed melt, while dry heat adds a little more texture to it — left uncovered too long in an oven, it can become leathery.

When the shoots are very tender, you can use the whole stem. The stems are best pickled, as they’re sour. Cooked, the stalks are mellower and soft, and reminiscent of cooked sorrel. Shoots lose their strong color the minute they meet heat, turning swamp green — but they still taste good. They work well with anything creamily bland, from dairy cream to coconut milk and eggs. Japanese knotweed is great in sauces; whipped into mashed potatoes; roasted with baby whole potatoes; and puréed into leek and potato soups. Many foragers like to use knotweed as they would rhubarb in the kitchen.

After the stems have matured and are too tough, the young unfurling leaf tips are still good to eat, with more crunch than the cooked stems. Sauté them briefly to add to omelets, to accompany spring meatballs; as a green stew with fava beans; or as a tart side to a rich main dish.

How to Collect and Prepare

To harvest the shoots in early spring, choose a spot where the previous season’s old canes — which are long, dry, brown, and hollow — stand tall or sprawl untidily. Avoid patches without canes but plenty of spindly shoots, because chances are good the clump was sprayed the year before.

Slice the youngest, plumpest green shoots off at the base. More mature, taller shoots can be sliced higher up. This is about harvesting meristems, the actively growing part of the plant, which will be most tender toward the tip (like an asparagus). Your knife will tell you where to slice; no effort should be required. Peel the membrane from tougher stems, and discard the joints between each hollow section if they’re tough. Very tender shoots can be eaten in their entirety.

Tiny, scented white flowers appear in summer. Cut whole flower stalks, and shake them gently to remove insects. Strip the flowers off the stalks at home. They’re a sour seasoning on a salad, or good for a fermented soda pop or cordial.

NOTE: This plant is highly invasive! Don’t chuck out your knotweed debris in the compost, or in the trash. Ideally, pieces of knotweed stem should be boiled to prevent them from taking root where they land. The tiniest pieces of stems can regenerate. Collect your knotweed trimmings in a pot, cover with water, and boil for 5 minutes, or until they’re dead.

Butter and Knotweed Sauce

Yields about 1/8 cup.

In springtime, the quickest thing I do with knotweed is chop it finely and melt it in some hot butter over medium heat. This quick, tart sauce is delicious on eggs, grilled chicken, and fish.

Ingredients

• 2 tablespoons butter
• 1-1/2 ounces Japanese knotweed, finely chopped
• Salt, to taste

Instructions

1. In a skillet, melt the butter over medium-high heat. When it foams, reduce the heat to medium and add the Japanese knotweed.
2. Cook for about 10 minutes, stirring a few times.
3. It will turn a khaki color and lose its crunch.
4. Season with salt.

Learn about and discover more edible invasives to use in your seasonal cuisine:

• Black Locust Foraging and Cooking Techniques
• Cooking with Burdock Root and Stems
• Foraging and Cooking with Invasive Species

Marie Viljoen is a forager, cook, and gardener in Brooklyn. Follow her at 66 Square Feet.

Reprinted with permission from Forage, Harvest, Feast: A Wild-Inspired Cuisineby Marie Viljoen, published by Chelsea Green Publishing.