Knotgrass: Benefits, Uses and Precautions

Dr. Boris Wydoff

Knotgrass, or common knotgrass, is a small plant in the buckwheat family. In herbal medicine, it has traditionally been used as a diuretic, astringent, and hemostatic herb. The herb has a particular place in traditional use for kidney diseases and urinary tract stones. Its composition includes flavonoid glycosides, tannins, vitamin C, and silicic acid.

What does this plant look like and how can you recognize it?

Knotgrass is also called bird's knotgrass. Its Latin name is *Polygonum aviculare*. It is an annual plant in the buckwheat family. It grows almost everywhere. You can find it along roadsides, in yards, wastelands, pastures, and even on sports fields. It needs only a small area of open soil.

The stems are prostrate or slightly ascending. They branch strongly from the base. The stems can reach 60–100 cm in length. Another botanical description gives a length of up to 60 cm.

Knotgrass has a feature that is important to know when harvesting it. Common knotgrass represents a complex of closely related forms and varieties that can be difficult to distinguish even for botanical specialists.

The leaves are small and numerous. They are elliptical or lance-shaped, up to 2 cm long. Their color is grayish or blue-green. The leaf stalk is very short. Small whitish membranous sheaths are found at the stem nodes. The flowers are small, white, or pink. They usually occur in groups of 2–5 in the leaf axils. After flowering, a small three-sided dark-brown nutlet appears.

Flowering lasts a long time. Different botanical descriptions give periods from May to September, while medicinal raw material is described as being collected from June until autumn. One reference considers the herb together with the roots to be the medicinal raw material and gives the name *Herba Polygoni avicularis*.

The plant has many folk names: green carpet herb, bird's buckwheat, sparrow grass, goose herb, and trampler. Knotgrass tolerates trampling well and therefore often grows where the soil is constantly under pressure.

Birds and livestock readily eat the plant. Young greens have also been used as food. They were added to soups, salads, purées, and fillings.

Where did the folk names for knotgrass come from?

The plant's names are connected with its appearance and hardiness. It was called “green carpet herb” because of its dense, low growth that forms a green cover. The name “trampler” is connected with the plant's ability to tolerate constant trampling.

Birds readily peck at the seeds and greens of knotgrass, which is why the names “bird's buckwheat” and “sparrow grass” became established. In some places it was called “goose herb.” Such a variety of names can be found in old descriptions of the plant.

How was knotgrass used in the past?

Knotgrass belongs to wild medicinal plants that were historically collected together with other natural raw materials. The harvested herb was supplied to pharmacies or sold to collectors. Old information about the medicinal herb trade mentions it among plants collected in southern regions and then sent into commerce.

The plant is also known in old medical traditions. Descriptions mention that knotgrass preparations were used by physicians of antiquity, including Hippocrates, Galen, and Dioscorides. They associated it with respiratory diseases, bleeding, and digestive disorders. In Chinese medical tradition, the plant was described as a tonic.

These historical records show how long the tradition of using the plant has existed, but they do not by themselves prove its effectiveness for a particular disease.

What substances does it contain?

The chemical composition of the herb is quite diverse.

According to herbal medicine references, flavonoid glycosides have been found in knotgrass. They include avicularin, hyperoside, and quercetin. When avicularin breaks down, it produces quercetin and arabinose. Traces of other flavonoids have also been found.

The herb contains tannins. One reference description gives their content at about 4 percent. Vitamin C, vitamin K, carotene, silicic acid, resins, mucilaginous substances, and traces of essential oil are also mentioned. Silicic acid occurs in soluble and insoluble forms. Oxymethylanthraquinones have been found in the roots.

Older descriptions associated silicic acid with the plant's effect on mineral deposits in the urinary tract. Knotgrass has also been described as increasing the elimination of sodium and chlorine from the body.

What is known about the flavonoids in knotgrass?

The flavonoid composition of knotgrass is described in more detail in reference books than simply as the presence of flavonoid compounds. Three quercetin derivatives are listed: quercetin, hyperoside, and avicularin. For avicularin, it is specifically noted that its breakdown produces quercetin and arabinose.

In addition to flavonoids, the herb contains about 4 percent tannins. Soluble and insoluble silicic acid, organic acids, resins, and mucilaginous substances are also described. Older pharmacognostic descriptions mention vitamin C and carotene.

This composition helps explain why knotgrass has been associated with several areas of traditional use in different sources. However, the presence of individual substances does not automatically mean a therapeutic effect for a particular disease.

What are the benefits of this plant?

The main traditional use of knotgrass is associated with the urinary system.

According to herbal medicine references, the herb has a diuretic effect. Studies of aqueous and alcoholic extracts noted an increase in urine output. This property is connected with the traditional use of knotgrass for kidney diseases and kidney stones.

An official reference description states that common knotgrass herb is used to help the passage of stones in urolithiasis. A moderate anti-inflammatory effect has also been described.

In folk herbal medicine, knotgrass was used as a diuretic for sand and stones in the kidneys and bladder. Older descriptions also mention reduced crystallization of mineral salts in the urinary tract.

Another traditional direction is its astringent and hemostatic action. Reference literature describes the use of knotgrass preparations as a uterine hemostatic remedy. Avicularin extract was produced in powder and tablet form.

Studies of aqueous and alcoholic extracts showed increased blood clotting. The same studies noted effects on the uterine muscles, a reduction in blood pressure, improved lung function, and increased urine output.

Reference books also list other actions of preparations made from the herb: antispasmodic, antiseptic, diaphoretic, antipyretic, expectorant, laxative, anthelmintic, and wound-healing effects. Some older descriptions associate knotgrass with the respiratory system. Studies noted an increase in the amplitude of respiratory movements and lung ventilation volume.

For external use in folk practice, fresh crushed herb was used. It was applied to wounds, bruises, and burns. The herb has also been described for use on old wounds that heal poorly.

Young greens also have food value. They were eaten as a vegetable, especially in the Caucasus. The leaves were used to prepare soups, purées, salads, and fillings.

How is it used?

Reference literature describes knotgrass in the form of a decoction, powder, and fresh juice. Aqueous extracts are also part of the traditional use of the plant. Fresh crushed herb was used externally.

One reference gives the following preparation method: 2 teaspoons of the herb are used for a cold infusion, after which it is briefly boiled.

Knotgrass was traditionally often included in mixtures with other plants. It appears in various old herbal formulas, including diuretic mixtures. One description specifically notes that in folk practice, plants were more often used in mixtures rather than individually.

A book that gives a recipe attributed to Dr. Breuss includes a kidney tea with knotgrass. The proportions are: horsetail — 15 g, nettle — 10 g, knotgrass — 8 g, St. John's wort — 6 g.

To prepare it, take a pinch of the chopped raw material. The book explains that a pinch is the amount held between the thumb, index finger, and middle finger. Steep the raw material in a cup of hot water for 10 minutes, then strain. Pour 2 cups of hot water over the strained residue again. The stated amount of the mixture is enough for about 3 weeks.

This is an old recipe from a book, not a universal modern treatment plan. If you have kidney stones, chronic kidney disease, swelling, or impaired kidney function, discuss its use with a doctor beforehand. Medical supervision is especially important if there is a possibility of a large stone or impaired urine flow.

Diuretic herbal remedies also require caution in people who already take diuretics. When combined with medicines that affect fluid and electrolyte excretion, the treatment plan should be assessed by a specialist.

Why is knotgrass often included in herbal mixtures?

In old manuals, knotgrass is rarely considered only as a standalone plant. It was included in different herbal formulas, whose composition depended on the intended use. In folk practice, it appears in diuretic mixtures together with horsetail, birch buds, corn silk, bearberry, St. John's wort, and other plants.

There are also more complex mixtures in which knotgrass was combined with herbs, flowers, and bark. One description for liver diseases included St. John's wort, knotgrass, wild chicory, immortelle, buckthorn bark, chamomile, and marigold flowers. Other knotgrass mixtures were intended for diuretic use.

The presence of knotgrass in such recipes reflects folk tradition but does not prove the effectiveness of every mixture for a particular disease. In addition, the more ingredients a mixture contains, the more important it is to consider their possible contraindications and interactions.

How are its fruits collected and stored?

The medicinal raw material is knotgrass herb. One reference calls the herb together with the roots medicinal raw material, while other descriptions collect the flowering herb. According to reference books, harvesting is carried out during flowering. Different periods are given: May to September, June until autumn, and July to September. The name of the medicinal raw material is *Herba Polygoni avicularis*. Some references specifically list the flowering herb.

Historically, knotgrass was considered wild medicinal raw material. It was harvested together with other plants and supplied to pharmacies or sold to collectors.

When collecting it yourself, it is especially important to identify the plant correctly. Common knotgrass belongs to a group of closely related forms that can be difficult to distinguish. Therefore, collect only a plant you know well.

When buying prepared raw material, check the botanical name on the package. This helps prevent confusion with other plants.

When is the best time to harvest the herb?

Harvesting periods differ slightly between references. For medicinal raw material, the flowering period from June until autumn is given. Another botanical guide gives the flowering period as May–September and the harvesting period also as May–September. Another reference gives June–August for knotgrass herb.

This does not mean there is one strictly fixed day for harvesting, but rather a flowering period. During this time, the herb is collected, and different sources describe both the flowering aerial parts and raw material collected together with the roots.

When collecting in nature, it is important to choose places where the plant is not obviously exposed to pollution. The fact that knotgrass grows near a road, in a yard, or on wasteland does not mean that a particular plant is suitable for medicinal use.

How can you distinguish knotgrass from related plants?

Identifying knotgrass can be difficult. *Polygonum aviculare* in the broad sense is described as a complex of dozens of closely related species and subspecies that can be difficult even for specialists to distinguish.

Use several features at once: a prostrate or slightly ascending, strongly branched stem; small alternate grayish-green leaves; membranous sheaths at the nodes; and small white or pinkish flowers in the leaf axils. After flowering, a three-sided dark-brown nutlet develops.

It is especially important not to confuse common knotgrass with Japanese knotweed — *Polygonum cuspidatum*. This is a different plant. For medicinal raw material, check the botanical name rather than relying only on the common word “knotgrass.”

How to find knotgrass (common knotgrass) abroad

If you live in the United States or Europe, look for knotgrass by its local name or by the Latin name *Polygonum aviculare*.

• USA: Knotgrass, common knotgrass, doorweed, birdweed.
• Germany: Vogelknöterich.
• France: Renouée des oiseaux, centinode.
• Latin: *Polygonum aviculare*; some packages may list *Centinodia herba*.

In what forms is it sold?

Most often, the dried aerial parts of the plant (*Herba*) are sold: loose chopped herb for infusion or tea, as well as tea bags, sometimes as part of herbal mixtures. Tinctures and liquid extracts are also available. Roots and fruits are usually not sold commercially, while capsules are less common than herb or tea.

Where to look

• USA: health food stores, specialty tea shops, online herb stores; knotgrass is uncommon in regular pharmacies.
• Germany: *Apotheke*, *Reformhaus*, online pharmacies, and herbal shops.
• France: *Pharmacie*, herbal shops (*herboristeries*), organic and natural food stores (*magasins bio*), and online stores.

Check the Latin name on the package, the plant part listed — aerial parts, stems, and leaves (*Herba*) — and the product category. In Germany, also check whether the product is labeled as medicinal tea (*Arzneitee*) or as a food product/supplement. You can also check for organic certification (*bio*, *kbA*, USDA Organic), country of origin, and information about purity testing.

Sales rules depend on the country: for example, in the USA knotgrass is sold as a dietary supplement, while in Germany pharmaceutical-grade *Arzneitee* is sold in pharmacies and regulated by BfArM.

Contraindications and precautions

Modern safety data on knotgrass are limited. Traditional use is mainly considered for adults and adolescents over 12 years of age. If you have an allergy or increased sensitivity to the plant, its use is contraindicated.

Special caution is needed when using it as a diuretic if a doctor has already advised you to restrict your fluid intake. This applies, in particular, to serious conditions in which fluid restriction is part of medical management.

The safety of knotgrass during pregnancy and breastfeeding has not been established because of insufficient data. Therefore, its use during these periods is not recommended. Knotgrass is not recommended for children under 12 because there is insufficient safety information. No known adverse effects were identified for the studied preparations in the EMA assessment. But this does not mean that adverse reactions are impossible. There is little information about overdose and toxicity in humans. Therefore, the absence of reports of serious reactions cannot be considered proof that large doses or concentrated extracts are safe.

No documented drug interactions have been identified in the available data, but clinical information is limited. If you take medicines regularly, discuss concentrated extracts, tinctures, and supplements with a doctor or pharmacist beforehand.

Already prescribed diuretics should be considered separately. When several remedies that affect fluid and electrolyte excretion are used at the same time, individual assessment of the treatment is necessary.

Do not confuse common knotgrass with Japanese knotweed — *Polygonum cuspidatum*. This is a different plant, and its safety data cannot automatically be applied to common knotgrass.

When should you see a doctor?

An allergic reaction after taking the plant requires stopping its use. Medical help is needed if symptoms are severe. Pregnancy and breastfeeding are periods when self-use of knotgrass is not recommended. Children under 12 should not be given the plant without specialist advice. If a person takes medicines regularly, especially several medicines at the same time, the use of concentrated herbal products should preferably be discussed with a doctor or pharmacist beforehand.

Chronic diseases require individual assessment. This is especially important when a doctor restricts fluid intake or prescribes diuretics.

Pain in the kidney area, blood in the urine, urinary retention, high fever, or a sudden deterioration in health require medical examination. With large stones, impaired urine flow can be dangerous, so you should not rely only on the plant's diuretic effect.

For diseases of the internal organs, diagnosis and treatment are determined by a doctor. Knotgrass may be considered only as a plant with traditional indications, not as a substitute for medical care.

Boris Wydoff — naturopath and author, Ph.D. in nutrition. For over fifty years I have helped people restore health through nutrition, cleansing and the power of the mind — in Europe, America and Asia. About the author →

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