Onopordum acanthium aka Cotton Thistle

Onopordum acanthium, or cotton thistle, belongs to the daisy family, Asteraceae. It is an upright biennial with a bold, spiny form. Its native range spans Europe, northwestern Africa and much of temperate Asia. It reaches east to Xinjiang and the western Himalaya. It grows on waste ground and in arable fields. Chalky and sandy sites suit it, and it avoids shade.

The RHS gives a garden height range of 8–13 feet [2.5–4 metres]. Its shorter description puts the height near 10 feet [3 metres]. Plants spread about 1.6–3.3 feet [0.5–1 metre] and form clumps. The long, oblong leaves carry spines and fine, web-like grey hairs. They reach about 1 foot [0.3 metres] in length. The plant sheds its leaves rather than keeping evergreen foliage. Rounded purple flower heads appear in summer. Each head measures about 0.16 feet [0.05 metres] across.

Give this thistle full sun and fertile soil that drains well. The RHS favours neutral to slightly alkaline ground. PFAF also records plants growing on slightly acid soils. Suitable soil types include chalk, loam and sand. Moisture can range from dry to moist, with good drainage. The RHS rates its hardiness H5 for UK conditions. PFAF lists USDA zones 5–9. Sow seed in spring or autumn, directly or in containers. A cold frame provides another place to raise seedlings.

Its tall form suits wild areas, gravel gardens and informal borders. Sources also suggest wildlife gardens and wildflower meadows. It attracts wildlife, but it can spread freely from seed. PFAF flags its potential to become a weed. Allow for that spread when choosing a planting site. The RHS says that it needs no pruning. Slugs and snails may attack it, though disease causes few problems.

Several parts have food uses, but they need preparation. Cooked flower buds can stand in for globe artichokes. Their small size makes preparation slow work. Peeled stems can serve as a cooked vegetable. Harvest leaves before flowering and remove their prickles before cooking. Petals provide yellow food colour and flavour. PFAF reports no known hazards; the sharp spines still need care. Other recorded uses include stem hairs for pillow stuffing. Seed oil has served as lamp fuel. PFAF also records medicinal uses for the plant and root. Those records do not establish safe or effective home treatment.