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A picture of a Cotton Thistle

Cotton Thistle

Onopordum acanthium

Also known as

Scotch Thistle, Argentine Thistle, Down Thistle, Giant Thistle, Musk Thistle, Oak Thistle, Queen Mary's Thistle, Silver Thistle, Star Thistle, Thistle-Upon-Thistle, Heraldic Thistle, Woolly Thistle, Scottish thistle

Full Sun
Light watering
Frost Hardy

H5

RHS hardiness

-15°C

Minimum temperature

Expected size

Height
Spread

4m

Max

1m

2.5m

Min

50cm

3 years to reach maturity

Flowering

  • spring
  • summer
  • autumn
  • winter

More images of Cotton Thistle

A close up of a purple Onopordum acanthium flower
A close up of a purple Onopordum acanthium flower

Cotton Thistle Overview

Onopordum acanthium is a biennial species with an upright growth habit, typically reaching a height of around 3m. Also known by the common names cotton thistle, Argentine thistle and down thistle amongst many others. Foliage is oblong in shape and grey in colour, leaves are spiny and cobwebby and measure around 30cm long. Flowers are rounded and thistly, coloured purple and these measure approximately 5cm across. This species is part of the Royal Horticultural Society “Plants for Pollinators” initiative to showcase plants which support pollinator populations by providing ample amounts of nectar and/ or pollen. A great choice for encouraging pollinating insect wildlife into your garden!

Common problems with Cotton Thistle

How to propagate Cotton Thistle

Seed

Sow in autumn or spring.

Special features of Cotton Thistle

Attractive flowers

Other uses of Cotton Thistle

Ornamental, wildflower/meadow, border, under shrubs

Garden Biennials

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