Japanese Knotweed Plant Care
Reynoutria japonica Houtt.
Updated · Sources · How we source care data
Reynoutria japonica, synonyms Fallopia japonica and Polygonum cuspidatum, is a species of herbaceous perennial plant in the knotweed and buckwheat family Polygonaceae. Common names include Japanese knotweed and Asian knotweed.
Every 3–5 days
Full sun to part shade
50–80°F
40–70%
At a glance
How do you care for Japanese Knotweed?
Water Japanese Knotweed every 3–5 days, letting the top layer of soil dry out between waterings, and give it full sun to part shade. It prefers temperatures of 50–80°F (10–27°C) and 40–70% humidity. Fertilize it every 8 months during the growing season. It is reported as toxic to pets, so keep it out of reach of pets.
Where Is the Japanese Knotweed Native To?
What Is the Japanese Knotweed?
Japanese Knotweed (Reynoutria japonica) belongs to the Polygonaceae family within the Reynoutria genus. Japanese Knotweed is native to East Asia in Japan, China and Korea. Japanese Knotweed is also known as Mexican Bamboo, Asian Knotweed.
Japanese Knotweed displays an aggressive spreading perennial growth habit, reaching up to 6 ft tall with a spread of approximately 10 ft. Japanese Knotweed produces small, greenish-white flowers in dense clusters.
Leaf size: approximately 6 inches.
How Often Should You Water a Japanese Knotweed?
Reynoutria japonica requires watering every 3–5 days. Allow the top layer of soil to dry between waterings to prevent root rot. Reduce watering frequency during winter when growth slows.
Watering Frequency
Every 3–5 days
Let soil partially dry between waterings
What Light Does the Japanese Knotweed Need?
Japanese Knotweed thrives in full sun to part shade.
Light Requirement
Full sun to part shade
What Temperature and Humidity Does the Japanese Knotweed Prefer?
Reynoutria japonica grows best at temperatures of 50–80°F. Japanese Knotweed prefers humidity levels of 40–70%.
Temperature
50–80°F
Humidity
40–70%
What Soil Mix Works Best for a Japanese Knotweed?
Rich, moist soil with good drainage. Good drainage is essential for Japanese Knotweed to prevent waterlogging, which leads to root rot and fungal issues.
How Often Should You Fertilize a Japanese Knotweed?
Feed Japanese Knotweed every 8 months during the growing season (spring and summer) with a balanced fertilizer diluted to the strength on the label.
Pause feeding in autumn and winter, when growth slows, and never fertilize dry soil — water first.
Fertilizing
Every 8 months
During the growing season
The PlantoScan app can remind you when to water and when to fertilize each plant.
How Do You Repot a Japanese Knotweed?
Divide and repot every 2-3 years in early spring. Choose a pot one size larger than the current container, and ensure it has drainage holes to allow excess water to escape.
How Do You Propagate a Japanese Knotweed?
Japanese Knotweed can be propagated through division, stem cuttings. Similar propagation techniques also apply to reynoutria ciliinervis plant care, which shares the same genus.
Is the Japanese Knotweed Toxic to Pets and Children?
Toxic (caution)
Reported as toxic in our plant data. Not verified by the ASPCA.
Toxic to humans and pets
This is a general caution, not veterinary or medical advice. If your pet ate a plant, contact your vet or animal poison control.
See all plants toxic to cats and plants toxic to dogs.
What Pests and Diseases Affect the Japanese Knotweed?
Japanese Knotweed is susceptible to japanese knotweed psyllid, japanese knotweed leaf miner. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.
Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.
What USDA Hardiness Zone Does the Japanese Knotweed Need?
Japanese Knotweed grows outdoors in USDA Zone 12a. It survives winters down to planting zone 12a. Japanese Knotweed is native to East Asia in Japan, China and Korea. In cooler regions, grow Japanese Knotweed as a houseplant or bring it indoors before the first frost.
Hardiness Zone
Zone 12a
Keep exploring plants
Japanese Knotweed is one of many species covered in the complete plant care and identification guide, which groups plants by genus, attribute, and popularity.
It belongs to the Reynoutria genus — compare its care with other Reynoutria species on PlantoScan.
Reynoutria is part of the Polygonaceae plant family — browse all Polygonaceae genera and species.
Japanese Knotweed thrives in bright light and direct sun — see other bright-light plants.
Related Plant Care Guides
Closely related plants with similar care requirements:
Sources
- Scientific name & taxonomy: Reynoutria japonica Houtt., family Polygonaceae (first published in Nat. Hist. 2(8): 640, t. 51, f. 1 (1777)) — World Flora Online record, IPNI name record.
- Pet toxicity: Japanese Knotweed is reported as toxic to pets in our plant data (not verified by the ASPCA), so treat it with caution. Checked against the ASPCA plant list; any other toxicity note on this page comes from PlantoScan's plant database.
- Hardiness zone: USDA Zone 12a, calculated from the plant's minimum temperature.
- Care values(watering, light, temperature, humidity, soil, fertilizing): PlantoScan's plant database, filtered by automatic plausibility checks — values that fail them are hidden. How we source and check plant data.
Spotted a mistake? Email info@upvision.media with the page link — we check and correct reported errors.
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