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Persicaria amphibia (Water knotweed)

Beginner
skill rating
1 hour care
per year
0.3m
Max height
2m
Max spread
2-5 years
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


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


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

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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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