• 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

Onopordum acanthium

cotton thistle

  • Other common names cotton thistle
    Argentine thistle

    down thistle
    giant thistle
    musk thistle
    oak thistle
    oat thistle
    Queen Mary's thistle
    Scotch thistle
    Scots thistle
    silver thistle
    star thistle
    thistle-upon-thistle

    see more
  • Family Asteraceae

  • Genus Onopordum are are upright biennials with a basal rosette of simple or pinnately lobed, grey-hairy leaves and large, thistle-like, pink or purple flower-heads in summer

  • Details O. acanthium is a robust, upright biennial to 3m tall, with oblong, spiny, cobwebby grey leaves to 30cm long, and rounded, thistle-like purple flower heads 5cm across in summer

  • Plant range Europe to C Asia

Characteristics

  • Foliage Deciduous

  • Habit Bushy

  • 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)

    H5

Colour

Sunlight

  • Full Sun

  • Aspect West-facing or South-facing

  • Exposure Sheltered

Soil

  • Sand

    Sand

  • Chalk

    Chalk

  • Loam

    Loam

  • MoistureWell-drained

  • SoilSand, Chalk, Loam

  • pHAlkaline, Neutral

Size

  • Ultimate height 2.5-4 metres

  • Ultimate spread 0.5-1 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Grow in fertile, well-drained neutral to slightly alkaline soil in full sun; may self-seed freely and is ideal for a gravel garden or wild areas

Propagation Propagate by seed in containers in a cold frame or in situ in autumn or spring

Suggested planting locations and garden types Flower borders and beds Cottage & Informal Garden Wildflower meadow

How to care

Pruning No pruning required

Pests Slugs and snails may damage the foliage

Diseases Generally disease free

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