Onopordum acanthium

RHS Plant Profile
cotton thistle

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cotton thistle RHS
cotton thistle RHS

Other common names

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, ysgallen gotymog

Plants for pollinators
Annual Biennial
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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

Position

Full sun

Soil Types

Chalk, Loam, Sand

Max Height

2.5-4 metres

Max Spread

0.5-1 metres

Size

Time to Maturity
2–5 years
Max Spread
0.5-1 metres
Max Height
2.5-4 metres

Growing Conditions

Chalk Loam Sand
Moisture
Well–drained
pH
Alkaline or Neutral

Position

Full sun
Aspect
West–facing or South–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)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
Yes
Foliage
Deciduous
Habit
Clump forming
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
Name Status
Correct
Plant Range
Europe to C Asia

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

  • Cottage and informal garden
  • Wildflower meadow
  • Wildlife gardens
  • Flower borders and beds

Pruning

No pruning required

Pests

May be susceptible to slugs and snails

Diseases

Generally disease-free