Photo: Eric SchmidtCC BY 4.0via iNaturalistresized / cropped
Douglas' Knotweed Plant Care
Polygonum douglasii Greene
Updated · Sources · How we source care data
This plant features striking lance-shaped leaves with vibrant red stems, originating from North America. Plant collectors are drawn to Polygonum douglasii for its unique foliage coloration and its ability to attract pollinators with its small white flowers.
Every 4–7 days
Full sun to part shade
60–75°F
50–70%
At a glance
How do you care for Douglas' Knotweed?
Water Douglas' Knotweed every 4–7 days, letting the top layer of soil dry out between waterings, and give it full sun to part shade. It prefers temperatures of 60–75°F (16–24°C) and 50–70% humidity. Fertilize it every month during the growing season.
Where Is the Douglas' Knotweed Native To?
What Is the Douglas' Knotweed?
Douglas' Knotweed (Polygonum douglasii) belongs to the Polygonaceae family within the Polygonum genus. Douglas' Knotweed is native to much of northern and western North America. Douglas' Knotweed is also known as Douglas's Smartweed.
Douglas' Knotweed displays a spreading ground cover growth habit, reaching up to 3 ft tall with a spread of approximately 2 ft. Douglas' Knotweed produces small, inconspicuous flowers in clusters.
Leaf size: approximately 4 inches.
How Often Should You Water a Douglas' Knotweed?
Polygonum douglasii requires watering every 4–7 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 4–7 days
Let soil partially dry between waterings
What Light Does the Douglas' Knotweed Need?
Douglas' Knotweed thrives in full sun to part shade.
Light Requirement
Full sun to part shade
What Temperature and Humidity Does the Douglas' Knotweed Prefer?
Polygonum douglasii grows best at temperatures of 60–75°F. Douglas' Knotweed prefers humidity levels of 50–70%. A pebble tray or humidifier helps maintain adequate moisture around the plant.
Temperature
60–75°F
Humidity
50–70%
What Soil Mix Works Best for a Douglas' Knotweed?
Moist, fertile soil with good drainage. Good drainage is essential for Douglas' Knotweed to prevent waterlogging, which leads to root rot and fungal issues.
How Often Should You Fertilize a Douglas' Knotweed?
Feed Douglas' Knotweed every month 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 month
During the growing season
The PlantoScan app can remind you when to water and when to fertilize each plant.
How Do You Repot a Douglas' Knotweed?
Divide and replant every 2-3 years. 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 Douglas' Knotweed?
Douglas' Knotweed can be propagated through seeds, division. Similar propagation techniques also apply to silver-sheathed knotweed plant care, which shares the same genus.
Is the Douglas' Knotweed Toxic to Pets and Children?
Pet safety not verified
The ASPCA does not list Douglas' Knotweed, so we can't confirm whether it is safe for cats and dogs. Keep pets from chewing it as a precaution.
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 Douglas' Knotweed?
Douglas' Knotweed is susceptible to aphids, caterpillars, leaf miners. 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 Douglas' Knotweed Need?
Douglas' Knotweed grows outdoors in USDA Zone 3a – 8b. It survives winters down to planting zone 3a. Douglas' Knotweed is native to much of northern and western North America.
Hardiness Zone
Zone 3a – 8b
Keep exploring plants
Douglas' 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 Polygonum genus — compare its care with other Polygonum species on PlantoScan.
Polygonum is part of the Polygonaceae plant family — browse all Polygonaceae genera and species.
Douglas' Knotweed thrives in bright light and direct sun — see other bright-light plants.
More Polygonum Species
Other Polygonum species in PlantoScan's care catalogue share similar watering, light, and soil preferences:
Sources
- Scientific name & taxonomy: Polygonum douglasii Greene, family Polygonaceae (first published in Bull. Calif. Acad. Sci. 1: 125 (1885)) — World Flora Online record, IPNI name record.
- Pet toxicity: Pet safety not verified: the ASPCA does not list Douglas' Knotweed, so we can't confirm whether it is safe for cats and dogs. Checked against the ASPCA plant list; any other toxicity note on this page comes from PlantoScan's plant database.
- Photo: Eric Schmidt, CC BY 4.0, iNaturalist — original.
- Hardiness zone: USDA Zone 3a – 8b, estimated from the plant's typical growing conditions.
- 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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