Persicaria polymorpha

RHS Plant Profile

alpine knotweed

RHS

Synonyms

Polygonum alpinum
Persicaria alpina (All.) H. Gross.
Aconogonon alpinum
Polygonum polymorphum
Persicaria polymorpha

Herbaceous Perennial

A tall, clump-forming semi-evergreen perennial to 1.5 with large, willowherb-like lance-shaped fine green leaves which turn to brown-orange in august, and strong stems bearing plumes of small, airy, delicately fragrant creamy-white flowers which flower over a long period in summer, followed by pinkish-red seed heads in late summer. Suitable for the back of a flower border. Holds well without the need for staking

Position

Full sun, Partial shade

Soil Types

Clay, Loam

Max Height

1.5-2.5 metres

Max Spread

1-1.5 metres

Size

Time to Maturity: 2–5 years
Max Spread: 1-1.5 metres
Max Height: 1.5-2.5 metres

Growing Conditions

Clay Loam

Moisture: Moist but well–drained or Poorly–drained
pH: Acid or Alkaline or Neutral

Position

Full sun Partial shade

Aspect: North–facing or West–facing or East–facing or South–facing
Exposure: Exposed or Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

H1A: under glass all year (>15C)
H1B: can be grown outside in the summer (10 - 15)
H1C: can be grown outside in the summer (5 - 10)
H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
H4: hardy through most of the UK (-10 to -5)
H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
H6: hardy in all of UK and northern Europe (-20 to -15)
H7: hardy in the severest European continental climates (< -20): H6
Drought Resistance: Yes

Colour & Scent

Fragrance Flower

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Polygonaceae
Native to GB/Ireland: No
Foliage: Semi evergreen
Habit: Clump forming
Potentially harmful: Contact with all parts may irritate skinthe sap may cause mild stomach upset if ingested. Wear gloves and other protective equipment when handling
Genus: A genus of annual or clump-forming perennial plants with terminal or axillary inflorescences carried on upright stems. Flowers are small, pale-coloured usually white or pink. Seeds are borne in achenes
Name Status: Correct
Plant Range: Eurasia

How to Grow

Cultivation

Grow in any moist soil in full sun or partial shade. Substantial mounds of foliage steadily increase in size, needing space and careful siting

Propagation

Propagate by division in spring or autumn or propagate by seed in spring

Suggested planting locations and garden types

City and courtyard gardens
Cottage and informal garden
Prairie planting
Rock garden
Gravel garden
Low Maintenance
Cut flowers
Flower borders and beds
Hedging and screens
Wall side borders

Pruning

No pruning required. Cut back after flowering

Pests

Generally pest-free

Diseases

Generally disease-free