Cirsium tuberosum aka Tuberous Thistle

Cirsium tuberosum, or tuberous thistle, is a European perennial. It belongs to the daisy family, Asteraceae. It grows in temperate regions and is native to Britain and Ireland. Its wild habitat includes damp grassland on lime-rich soils. Gardeners can grow it in beds or wildflower meadows. The RHS also suggests it for wildlife gardens.

Green leaves form a mound from a basal rosette. Their edges have soft teeth. The plant loses its leaves for winter. The RHS gives a mature height of 1.6–3.3 feet [0.5–1 metre]. Its description places the leafy mound around 2 feet [0.6 metres] high. The spread figures differ within the same source. The size table gives up to 0.3 feet [0.1 metres]. The description gives a wider spread of 1 foot [0.3 metres]. Plants reach their full size in one to two years.

Purple-pink, thistle-like flowers appear from June through August. These summer blooms rise above the green leaf mound. Seed fluff has a practical use as tinder. Plants For A Future records this use for the species. The plant can also grow from seed sown outdoors. The evidence gives no detailed account of its fruit.

Choose full sun and soil that drains well but stays moist. The RHS lists chalk, clay, loam, and sand as suitable soils. It also accepts acid, neutral, and alkaline conditions. Both exposed and sheltered sites can suit this plant. South-facing and west-facing positions appear among the RHS choices. Its H5 rating indicates hardiness across most of the UK. This rating covers winter lows of 5–14°F [−15 to −10°C]. It needs no pruning, and the RHS reports few pest or disease problems.

The root is edible when cooked and can be stored over winter. Plants For A Future gives it an edible-use score of three out of five. Its taste can be slightly bitter. Some roots have a strong aroma that makes them less pleasant. The root contains inulin, which people cannot digest. Gut fermentation can therefore cause gas in some people. The source lists no known hazards, but this is not proof of complete safety. It records no known medicinal uses and does not flag weed potential.