Wild edibles: how to find and eat Japanese knotweed
One of the most invasive plants in North America tastes like tart rhubarb for a few weeks each spring. Learn it in summer, harvest it in April.
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Eat no wild plant until it has been positively identified, by an experienced forager or a reliable regional field guide, and eat only a small amount the first time. Some poisonous plants look close enough to edible ones to fool a beginner.
Japanese knotweed (Reynoutria japonica, also listed as Fallopia japonica) grows along roadsides, riverbanks and vacant lots across most of the United States. Native to East Asia, it arrived as an ornamental in the late 1800s and escaped. Its rhizomes form dense thickets and can crack paving and foundations. It is also good to eat, and no forager needs to worry about overpicking it.
How to identify it
By the time most people notice the plant it is too tough to eat, so learn a stand in summer and come back the following spring.
Spring shoots
Shoots come up in April or May, depending on the region, and can grow more than an inch a day. Young shoots are stout, smooth and hollow, green to reddish with purple speckling, with distinct joints like bamboo. At each joint a thin papery sheath wraps the stem. The first leaves emerge rolled and reddish-purple.
Summer and fall
By midsummer a stand is 6 to 15 feet tall and looks like one huge shrub, since it grows from a single linked root system. Stems zigzag slightly from joint to joint, leaves are broad, 4 to 6 inches long with a flat base, and in late summer sprays of tiny creamy-white flowers hang from the joints.
Late fall and winter
After frost the stems die back to hollow, reddish-brown canes that often stand all winter, marking the spot for next year.
Look-alikes and cautions
- Pokeweed (Phytolacca americana) also sends up reddish shoots in spring and is poisonous, especially the roots and mature stems. Pokeweed stems lack the bamboo-like joints and papery sheaths, and are not hollow between joints. If there is any doubt, leave it.
- Knotweed is a favorite target for herbicide spraying. Harvest only where you know it has not been treated, and skip any stand that looks withered or scorched.
- Like rhubarb and spinach, it contains oxalic acid. Eat it in moderation, and avoid it if you have kidney stones, gout or have been told to limit oxalates.
- Pieces of stem and root can grow into new plants. Do not compost trimmings or drop them in another spot; the UConn invasive plant factsheet recommends bagging cut material and putting it out with the trash.
How to eat it
Harvest shoots under about 12 inches, snapping them off near the ground. Once the stems turn woody they are past their best. Raw, the shoots are crisp and sour, much like rhubarb, though cooking is the better way to eat them, and they can replace rhubarb in pies, crumbles and jam.
Apple and knotweed compote (one serving)
- 2 cups sliced apples
- 1 cup sliced young knotweed shoots
- 1/2 cup apple juice
- Sugar or honey to taste (optional)
Simmer everything, covered, for 10 to 15 minutes until the apples are soft. Serve warm.
Nutrition and medicinal claims
Foraging guides list the shoots as a source of vitamins A and C, potassium, phosphorus, zinc and manganese. The roots are rich in resveratrol, the compound in grape skins, and supply most resveratrol supplements.
Herbalists promote knotweed root for Lyme disease, arthritis and inflammation. None of those uses has been established in clinical trials, so talk to a doctor before treating it as medicine.