How do I get rid of it?

Complete eradication usually requires repeated professional herbicide application over several years.

No, even small fragments of the root or stem can sprout into new plants.

Plant guide

Japanese knotweed.

Reynoutria japonica

Pronounced ray-NOO-tree-uh juh-PON-ih-kuh

Also known as Asian Knotweed, Asiatic Knotweed, Itadori knotweed, Japanese Knotweed, Japanese fleece flower, Mexican bamboo, Mexican-bamboo

Japanese knotweed is a highly invasive herbaceous perennial that spreads aggressively through an extensive underground rhizome system. It is widely considered a noxious weed due to its ability to damage infrastructure and outcompete native flora. Please be aware that this plant is strictly regulated in many regions and should not be planted.

At a glance

Care level: Easy
Plant type: Herbaceous perennial
Light: Full sun to partial shade
Indoor light: Bright indirect
Water: Every 7 to 14 days
Mature size: 2 to 3 meters
Growth rate: Fast
Hardiness: USDA 4 to 9
Bloom time: Late summer to early autumn

Care

This plant requires no care and is extremely difficult to eradicate once established. Watch for new shoots emerging from the ground, as they can grow through concrete and asphalt. Control efforts usually involve professional chemical treatment or repeated mechanical removal over several years.

Watering: It is highly drought tolerant once established.
Feeding: Fertilizing is unnecessary as it thrives in poor soil conditions.
Pruning: Stems die back to the ground in winter and should be cleared if they pose a hazard.
Repotting: Do not grow this plant in containers as it will easily break through them.
Soil: Adaptable to most soil types
Soil pH: 5.0 to 8.0
Temperature: -30 to 35°C
Humidity: 40 to 80%
Drought tolerance: High
Lifespan: Perennial, can persist for decades.
Fragrance: Light
Deer and rabbits: High

Safety

People: The plant contains oxalates which can cause irritation if consumed in large quantities.
Pets: This plant is generally considered non-toxic to cats and dogs.
Children: The hollow stems are brittle and can break easily, posing a minor injury risk if children play inside dense thickets.
Contact allergens: The stems can cause minor skin irritation in sensitive individuals.
Airborne allergens: The pollen may trigger allergic reactions in some people during late summer.
Edibility: While young shoots are sometimes eaten, this plant is highly invasive and often treated with herbicides, making wild foraging extremely dangerous.

How to identify it

Bamboo like hollow reddish stems
Heart shaped or triangular leaves
Small creamy white flower clusters
Extensive underground rhizome network

Height: 1 to 3m
Spread: 1 to 5m
Leaves: green, deciduous
Flowers: white, cream, 0.5 to 1cm
Fruit: brown, Autumn

Problems to watch for

Leaf SpotCommon
AphidsUncommon
Powdery MildewUncommon
Root RotRare

By symptom

Plant problems by symptom

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Growing it

Propagation: division, rhizome cuttings
When to plant: spring, autumn
Overwintering: The foliage dies back completely to the ground after the first frost. No winter protection is needed as the rhizomes are extremely hardy.
In containers: This plant should never be grown in containers as it is highly invasive and poses a severe risk to the environment.

Do not propagate

Do not plant this species.
If found, contact local authorities for removal advice.

Do not plant this species anywhere as it will aggressively overtake all other plants in your garden.

Similar species

Giant Knotweed · It is a larger, closely related invasive species with similar growth habits.

Science

Family: Polygonaceae
Genus: Reynoutria
Order: Caryophyllales
Class: Magnoliopsida
Native range: East Asia including Japan, China, and Korea.
Conservation: It is classified as a highly invasive weed in many countries and should never be planted intentionally.

It thrives in disturbed soils and riparian areas where it outcompetes native vegetation by forming dense, light-blocking monocultures.

Value to wildlife: late season nectar source
Pollinators: bees
Uses: erosion control, honey production

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 5/9
Light: 7/9
Temperature: 5/9
Moisture: 5/9
Nutrients: 6/9

Taxonomy resolved against GBIF.

Questions people ask

How do I get rid of it?: Complete eradication usually requires repeated professional herbicide application over several years.
Can I compost it?: No, even small fragments of the root or stem can sprout into new plants.

Where the name comes from

The name Reynoutria honors the Dutch botanist K.F. von Reynout. The species name japonica refers to its native range in Japan.

Good to know

It can grow up to 10 centimeters in a single day during peak season.
The roots can extend up to 3 meters deep and 7 meters horizontally.
It was introduced to Europe and North America as an ornamental plant in the 19th century.
It is nearly impossible to eradicate once established in a garden.

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This guide was generated with AI on September 26, 2026 and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.