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Herbaceous Perennial

Koenigia × fennica 'Johanniswolke'
  • RHS AGM

knotweed 'Johanniswolke'

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

Synonyms
Persicaria × fennica 'Johanniswolke'
Aconogonon 'Johanniswolke'
see morePersicaria polymorpha 'Johanniswolke'
Persicaria alpina misapplied
Koenigia alpina misapplied

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Size
Ultimate height
1.5–2.5 metres
Time to ultimate height
2–5 years
Ultimate spread
1–1.5 metres
Growing conditions
Clay
Loam
Moisture
Moist but well–drained, Poorly–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Green
Summer Cream White Green Pink Red
Autumn Green
Winter
Position
  • Full sun
  • Partial shade
Aspect

East–facing or North–facing or South–facing or West–facing

Exposure
Exposed or Sheltered
Hardiness
H6
Botanical details
Family
Polygonaceae
Native to the UK
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

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

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