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Persicaria amphibia (Water knotweed)
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1 hour care
per year
per year
0.3m
Max height
Max height
2m
Max spread
Max spread
2-5 years
To maturity
To maturity
Plant details
Botanical name
Persicaria amphibia
Other names
Water knotweed, Polygonum amphibium, Water smartweed, Amphibious bistort, Amphibious knot grass, Floating polygonum, Ground willow, Heart's ease, Water buckwheat, Water willow, Willow grass
Genus
Persicaria Persicaria
Species
P. amphibia - P. amphibia is a variable, vigorous, moisture-loving or aquatic, rhizomatous perennial with long, usually lance-shaped, mid- to dark green leaves and, from midsummer into autumn, erect stems bearing dense, terminal clusters of five-petalled, pink flowers followed by glossy, brown fruit.
Persicaria amphibia is: Deciduous
Habit
Spreading
Flower
Pink in Summer; Pink in Autumn
Foliage
Green in Spring; Green in Summer; Green in Autumn
How to care
Watch out for
Pests
Generally pest-free.
Specific pests
Waterlily Pests (beetle, aphid, leaf-mining midges) Waterlily Pests (beetle, aphid, leaf-mining midges)
Diseases
Generally disease-free.
General care
Pruning
Divide every few years in spring to avoid congested plants. Cut back in late autumn after the leaves die down.
Propagation methods
Division
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Where to grow
Persicaria amphibia (Water knotweed) will reach a height of 0.3m and a spread of 2m after 2-5 years.
Suggested uses
Beds and borders, Cottage/Informal, Low Maintenance, Prairie planting
Cultivation
Grow in reliably moist, fertile soil or in water up to 45cm deep in full sun or partial shade. Will tolerate depths of 2-3 meters. Grow in baskets of loam to restrict spread. Site carefull as may become invasive. Not suitable for small ponds.
Soil type
Clay, Loamy, Sandy
Soil drainage
Boggy damp conditions, Moisture-retentive, Pond/In water
Soil pH
Acid, Alkaline, Neutral
Light
Partial Shade, Full Sun
Aspect
South, East, West
Exposure
Exposed, Sheltered
UK hardiness Note: We are working to update our ratings. Thanks for your patience.
Hardy (H4)
Companion plants
We do not currently have companion plants added for this plant.
Botanical name
Persicaria amphibia
Other names
Water knotweed, Polygonum amphibium, Water smartweed, Amphibious bistort, Amphibious knot grass, Floating polygonum, Ground willow, Heart's ease, Water buckwheat, Water willow, Willow grass
Genus
Persicaria Persicaria
Species
P. amphibia - P. amphibia is a variable, vigorous, moisture-loving or aquatic, rhizomatous perennial with long, usually lance-shaped, mid- to dark green leaves and, from midsummer into autumn, erect stems bearing dense, terminal clusters of five-petalled, pink flowers followed by glossy, brown fruit.
Foliage
Deciduous
Habit
Spreading
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Colour
Flower
Pink in Summer; Pink in Autumn
Foliage
Green in Spring; Green in Summer; Green in Autumn
How to care
Watch out for
Pests
Generally pest-free.
Specific pests
Waterlily Pests (beetle, aphid, leaf-mining midges)
Diseases
Generally disease-free.
General care
Pruning
Divide every few years in spring to avoid congested plants. Cut back in late autumn after the leaves die down.
Propagation methods
Division
Monthly care advice
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Where to grow
Persicaria amphibia (Water knotweed) will reach a height of 0.3m and a spread of 2m after 2-5 years.
Suggested uses
Beds and borders, Cottage/Informal, Low Maintenance, Prairie planting
Cultivation
Grow in reliably moist, fertile soil or in water up to 45cm deep in full sun or partial shade. Will tolerate depths of 2-3 meters. Grow in baskets of loam to restrict spread. Site carefull as may become invasive. Not suitable for small ponds.
Soil type
Clay, Loamy, Sandy
Soil drainage
Boggy damp conditions, Moisture-retentive, Pond/In water
Soil pH
Acid, Alkaline, Neutral
Light
Partial Shade, Full Sun
Aspect
South, East, West
Exposure
Exposed, Sheltered
UK hardiness Note: We are working to update our ratings. Thanks for your patience.
Hardy (H4)
USDA zones
Zone 8, Zone 7, Zone 6, Zone 5, Zone 4
In order to add a note on this plant, please add this plant to your plant lists.
| This plant likes... | Garden match | |
| Soil types: | Clay, Loamy, Sandy | Tell us... |
| Soil drainage: | Boggy damp conditions, Moisture-retentive, Pond/In water | Tell us... |
| Soil pH: | Acid, Alkaline, Neutral | Tell us... |
| Light: | Partial Shade, Full Sun | Tell us... |
| Aspect: | South, East, West | Tell us... |
| Exposure: | Exposed, Sheltered | Tell us... |
| Hardiness: | Hardy (H4) | Tell us... |
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