Koenigia × fennica 'Johanniswolke'

RHS Plant Profile

knotweed 'Johanniswolke'

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Synonyms

Persicaria × fennica 'Johanniswolke'
Aconogonon 'Johanniswolke'
Persicaria polymorpha 'Johanniswolke'
Koenigia alpina misapplied
Persicaria alpina misapplied

Herbaceous Perennial

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A tall, clump-forming perennial to 2m with large, lance-shaped green leaves and strong, upright stems producing plumes of small, intensely fragrant, creamy-white flowers over a long period in summer, followed by pinkish-red seed heads. 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: East–facing or North–facing or South–facing or West–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

Colour & Scent

Fragrance Flower

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Polygonaceae
Native to GB/Ireland: No
Foliage: Deciduous
Habit: Clump forming
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: Accepted

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 See https://www.rhs.org.uk/plants/trials-awards for further information about RHS plant trials and awards

Propagation

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

Suggested planting locations and garden types

Architectural
Cottage and informal garden
Flower borders and beds

Pruning

No pruning required. Cut back after flowering

Pests

Generally pest-free

Diseases

Generally disease-free