• AGM plants

    AGM plants have been through a rigorous trial and assessment programme. They are:

    • Excellent for ordinary use in appropriate conditions
    • Available to buy
    • Of good constitution
    • Essentially stable in form & colour
    • Reasonably resistant to pests & diseases

Persicaria affinis 'Superba'

knotweed 'Superba'

AGM plants

AGM plants have been through a rigorous trial and assessment programme. They are:

  • Excellent for ordinary use in appropriate conditions
  • Available to buy
  • Of good constitution
  • Essentially stable in form & colour
  • Reasonably resistant to pests & diseases
knotweed 'Superba'

© © RHS 2002

  • Other common names knotweed 'Superba'

  • Synonyms Persicaria affinis 'Dimity'
    Polygonum affine 'Dimity'

    Polygonum affine 'Superbum'

    see more
  • Family Polygonaceae

  • Genus Persicaria can be annuals, herbaceous or evergreen perennials or sub-shrubs with simple leaves and small bell-shaped white or pink flowers in long-lasting spikes or panicles

  • Details 'Superba' is a semi-evergreen perennial forming a wide mat to 20cm in height, with dark green, elliptic leaves and erect spikes of small pale pink flowers that deepen to crimson with age

Characteristics

  • Foliage Semi-evergreen

  • Habit Mat forming

  • 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)
    Old hardiness ratings

    While we update our systems with the new hardiness ratings you may still see old hardiness ratings in your search results. These are denoted as 'Old'.

    • H1 - Requires heated glass
    • H2 - Requires unheated glass
    • H3 - Hardy outside in some regions of the UK
    • H4 - Hardy throughout the UK
    • H1 + H3 - Requires heated glass but may be grown outside in summer

    For full details of the hardiness ratings see

    see more

    H5

Colour

Sunlight

  • Full Sun

  • Partial Shade

  • Aspect South-facing or West-facing or East-facing or North-facing

  • Exposure Exposed or Sheltered

Soil

  • Chalk

    Clay

  • Chalk

    Loam

  • MoisturePoorly-drained, Moist but well-drained

  • SoilClay, Loam

  • pHNeutral, Acid, Alkaline

Size

  • Ultimate height

    0.1-0.5 metres

  • Ultimate spread

    0.5-1 metres

  • Time to ultimate height

    5-10 years

How to grow

Cultivation Grow in any moist soil in full sun or partial shade.

Propagation Propagate by division in spring or autumn

Suggested planting locations and garden types Flower borders and beds Garden Edging Ground Cover Cottage & Informal Garden Rock Garden

How to care

Pruning Cut back after flowering

Pests Generally pest free

Diseases Generally disease free

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