Cotton Thistle

Description

Onopordum acanthium, commonly known as Cotton Thistle, Scottish Thistle or Scotch Thistle, is a striking biennial plant known for its robust growth and bold appearance. It features large, coarse, spiny leaves and distinctive spiny-winged stems that make it stand out in any landscape. Beyond its dramatic form, Cotton Thistle also supports wildlife—its foliage serves as a valuable food source for the caterpillars of various Lepidoptera species, contributing to local biodiversity.

It produces a large rosette of spiny leaves in the first year. The plants typically germinate in the autumn after the first rains and exist as rosettes throughout the first year, forming a stout, fleshy taproot that may extend down 30 cm (12 in) or more for a food reserve.

Most seeds germinate in autumn after the first rains, but some seeds can germinate year-round under favourable moisture and temperature conditions. Seeds that germinate in late autumn become biennials. But when they germinate earlier, they can behave as annuals.

Cotton Thistle (Onopordum acanthium) typically flowers in the UK from June to August. During this period, it produces large, purple disc-floret flower heads that are highly attractive to pollinating insects such as bees and butterflies. The tall flowering stems and bold blooms make it a standout feature in wildflower meadows, dry grasslands, and wildlife-friendly gardens throughout the summer months.