• 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

Centaurea atropurpurea

very dark purple knapweed

  • Other common names very dark purple knapweed

  • Synonyms Centaurea benoistii misapplied
    Cheirolophus benoistii misapplied

  • Family Asteraceae

  • Genus Centaurea may be annuals, perennials or subshrubs, with simple or pinnately lobed leaves and showy thistle-like flowers-heads, often with enlarged outer florets

  • Details C. atropurpurea is a clump-forming perennial to 1m with deeply divided, grey-green leaves. The deep red flowers emerge from bronze-coloured, scaly buds on strong stems in summer

  • Plant range C Balk., Romania

Characteristics

  • Foliage Deciduous

  • Habit Clump-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)

    H7

Colour

Sunlight

  • Full Sun

  • Aspect South-facing or West-facing

  • Exposure Exposed or Sheltered

Soil

  • Chalk

    Chalk

  • Sand

    Sand

  • Loam

    Loam

  • MoistureWell-drained

  • SoilChalk, Sand, Loam

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height 0.5-1 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Any well-drained soil in full sun; good drought resistance. A fairly dry, poor soil is best as plants can be invasive if soil is rich and moist

Propagation Propagate by seed sown in pots in a cold frame in spring or propagate by division in spring or autumn

Suggested planting locations and garden types Flower borders and beds Cut Flowers Drought Resistant Cottage & Informal Garden Wildlife Gardens Prairie Planting Gravel Garden Coastal

How to care

Pruning Deadhead regularly to prolong flowering

Pests Generally pest free

Diseases May be affected by powdery mildews

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