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There are around 1,200 knotweed species in total and the question of whether knotweed is poisonous keeps coming up. Many are cultivated in Germany, which is of particular concern to pet owners. The good news first: knotweed plants are non-toxic, neither for humans nor for pets. However, the problem is the oxalic acid content, which is not present in every species.


What toxins do knotweed varieties contain?

No type of knotweed contains substances that are toxic to humans. The plants are even used in homeopathy as a remedy. Excessive consumption of the plant only becomes problematic when it contains too much oxalic acid.
What can oxalic acid cause?

  • weakening of the connective tissue
  • weakening of the bones
Rhubarb, Rheum rhabarbarum

Oxalic acid in Persicaria

All known knotweed varieties contain oxalic acid. Humans can occasionally compensate for this without any problems. However, if large amounts of oxalic acid are ingested, this is particularly problematic for small children, pets and people who are already ill. Risk groups include:

  • People with gout or osteoarthritis
  • children
  • pregnant women

These people should avoid consuming oxalic acid. The same applies to people who suffer from kidney disease or who form urinary stones.

tip: The proportion of oxalic acid depends on the time of harvest. If harvested late in the year, the proportion is significantly higher!

consumption tip: If knotweed is consumed together with milk, the oxalic acid content can be neutralized.


Is knotweed poisonous?

For children and adults

No currently known species of knotweed is poisonous! However, small children should not consume large amounts of it, as the body is not yet able to break down and process oxalic acid.

For animals

Those who have pets often let them roam freely in the garden. This naturally raises the question of what influence the consumption of knotweed plants has on pets. In principle, no toxicity is known here either, but not all animals can process the oxalic acid content equally well.

These animal species should not be fed with Persicaria:

  • turtles
  • Chicken
  • sheep
  • Rabbits
  • horses

However, turtles can process small amounts of oxalic acid. Caution is required, however, because there is a risk of consuming large amounts kidney damage. However, feeding in moderation is not a problem.


If your dog has eaten knotweed, there is no reason to panic. Neither the plants themselves nor the oxalic acid are harmful to dogs.


Anyone who owns a cat should ensure that it does not regularly have access to and consume knotweed plants. Because the cat's body cannot break down oxalic acid and regular consumption carries the risk of kidney disease.


However, horses can easily process small amounts of oxalic acid. However, if knotweed is ingested in excess, it can lead to a drop in calcium levels and diarrhea.

rabbits and chickens

Rabbits do not tolerate oxalic acid well and should therefore not be fed knotweed. However, the situation is different with chickens. If they have calcareous feed available, they can process oxalic acid.


However, in sheep, excessive consumption of oxalic acid can lead to severe diarrhea and later to a lack of calcium. Therefore, only extremely small amounts should be fed to avoid symptoms.

First aid for symptoms

If an animal or a person in the risk group has consumed too much of the knotweed plant, there is no need to panic at first. Oxalic acid is not toxic, but can only lead to a few, mostly mild symptoms. If a pet exhibits symptoms related to consumption of the plant, the veterinarian should still be consulted. Small children and weakened people should then be taken to a doctor as a precaution. When home remedies are suitable:

  • Neutralization of oxalic acid with milk
  • Drink plenty of water to flush the kidneys
  • keep calm

4 edible knotweed plants and their ingredients

Among the knotweed species, there are better-known and lesser-known varieties. The most common types include:


  • bot. Rheum rhabarbarum
  • Edible part: petioles
  • contains vitamin C, iron, phosphorus, potassium
  • Harvest time between April and June
  • usable for sweet and savory dishes
  • no toxicity


  • bot. fagopyrum
  • Edible part: seeds
  • contains: vitamin E, B1, B2, iron, calcium, magnesium, lysine
  • Harvest time between August and September
  • usable as flour, porridge, flatbread, soup
  • no toxicity


  • bot. Rumex
  • Edible part: leaves
  • contains: vitamins A and C
  • Harvest time between April and June
  • Can be used as a substitute for spinach, salad
  • no toxicity
Blood dock, Rumex sanguineus

meadow knotweed

  • bot. Polygonum bistora
  • Edible part: leaves, seeds, shoots
  • contains: vitamin C and starch
  • Harvest time: leaves - March to April, seeds: August to September
  • usable as: spinach substitute, flour, salad
  • no toxicity

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