Knotgrass (Polygonum aviculare), also known as knotweed, is an annual summer herb and type of buckwheat that is native to Europe and Asia and naturalized just about everywhere else, including most of the U.S. This weedy plant thrives in disturbed fields, gravelly patches along the roadside and other wayside places, as long as there is plenty of sun. It may seem delicate because of its small stature and low-growing habit, but it is remarkable resilient and aggressive. In fact, a single plant can sprawl more than three feet across the ground. Another reason for the plant’s success is that its seeds, transported by wind and birds, can lie dormant in the ground for years, if necessary, until conditions are favorable for germination.
What’s in a name?
As a member of the dock family knotgrass has a lot of famous relatives, most notably Japanese knotweed and yellow dock. It is also known by a wide variety of nicknames, a small sampling of which includes jointgrass, pigweed, doorweed, lowgrass, birdweed and nine-weed. The plant’s scientific name is descriptive of its physical characteristics. The genus name of “Polygonum” is derived from “poly” and “gonu,” which respectively mean “many” and “knees.” This is a reference to the swollen knots or “joints” from which new leaflets and pinkish-white, petal-less flowers emerge. The species name of "aviculare" comes from the word “avis,” which translates to “bird” and refers to the beak-like shape of the leaves.
Knotweed has been used as food for all of recorded human history. There is evidence that Tollund Man, a mummified corpse dating to the 4th century BCE discovered in a Danish bog in 1950, enjoyed knotgrass seeds as part of his last meal.
On a mission to harvest some knotgrass, students Harry Potter and Hermione Granger dared to venture into The Forbidden Forest that surrounded Hogwart’s School of Witchcraft and Wizardry. The herb was an ingredient in Polyjuice Potion, an elixir that allowed a person to take the form of another that required advanced skills and hard-to-find ingredients to produce.
“This is the most complicated potion I’ve ever seen. Lacewing flies, leeches, fluxweed, and knotgrass. Well, they’re easy enough.” – Hermoine Granger
In Asia, where the herb is known as rau dang, knotgrass is commonly paired with lemongrass and other herbs and spices and used in soups, “hot pot” stews and other dishes that contain vegetables, meats and seafood. The herb is also served fresh alongside many dishes. In Vietnam, knotgrass is an ingredient in a traditional soup that consists of fermented fish and noodles called Bun mam.
The entire plant is edible, and has a pleasant, slightly nutty flavor. The young leaves and stems are eaten raw in salads or steamed as a vegetable. The dried and ground seeds are added to flours to make bread and other baked goods. Knotgrass is also a good source of fiber, protein, minerals and vitamins.
Knotgrass contains a number of flavonoids that are responsible for its medicinal actions, such as avicularin, astragalin, jugalamin and myricitrin. These agents work together synergistically to provide the following benefits:
Anthelmintic: expels internal parasites
Astringent: tightens tissues
Diuretic: increases urine output
Emollient: softens skin
Expectorant: thins mucous
Febrifuge: reduces fever
Vulnerary: speeds healing of wounds
Hemostatic: stops bleeding
Some of the most notable uses of knotgrass is in mouth rinses (made from the whole plant) to help reverse gingivitis. While the herb’s flavonoids exert an anti-inflammatory effect on the gums to reduce soreness and swelling, they also deter plaque formation by inhibiting the metabolism of glucose.
Other Common Uses
Apply the bruised fresh leaves as a poultice for scrapes, insect bites and other minor skin irritations.
Use the herb to make a salve for hemorrhoids.
Infuse the herb in oil for use in homemade lotions and creams for dry skin.
Tincture the plant and add a dropperful to morning tea or juice as a mild diuretic.
Brew into tea for fever (especially paired with catnip), lung congestion, or to simply enjoy.
Fill a small mason jar with fresh or dried knotgrass, leaving a half-inch space at the top. Cover the herbs with vodka (the highest proof you can find). Let the alcohol-herb mixture steep in a sunny place for 4 to 6 weeks, turning the jar once each day. Strain and pour the reserved liquid into amber bottles with droppers. Store in a cool, dark place.
Knotgrass Ginger & Spice Tea
This tea is nice served warm, but it also makes an excellent iced tea for the warm weather months. Keep some in the fridge to enjoy after an afternoon of gardening.
4 cups filtered water
½ cup knotgrass (leaves, stems, flowers)
2 teaspoons freshly grated ginger
1 teaspoon orange zest
1 cardamom pods, crushed
1 whole cinnamon stick
Combine all ingredients in a medium saucepan. Bring to the boil, then reduce heat and simmer for 15-20 minutes. Remove from heat and cover; let steep for 5 minutes. Strain and serve the tea with honey and sliced lemon, if desired.