How to Grow and Care for Cottonthistles

Scotch thistle (Onopordum acanthium) is considered to be a noxious weed in many parts of the world. Dense colonies of this plant interfere with animals' ability to graze and limit their access to water. However, its large blooms and unique leaves have led some people to grow it ornamentally.

Illyrian cottonthistle is an attractive flowering plant. While it is on the Federal Noxious Weed and Seed List, it is also used as an ornamental flower and in agricultural containment. It is a self-seeding species. Each plant can produce up to 40,000 seeds that may contaminate wool and other agricultural produce and equipment.

Bull cotton thistle is considered a noxious weed in many US regions. It is hard to miss this plant's big purple flowerheads, sporting the characteristic thistle appearance. Although similar to its close relative O. Illyricum, bull cotton thistle's leaves are green and smooth, not hairy.

Onopordum cynarocephalum is a thistle that comes from the Middle East, with flowers that feed many varieties of butterflies and moths. The name "onopordum" comes from the Greek words meaning "farting donkey" because it was believed to make donkeys pass gas. "Cynarocephalum" comes from the Latin words meaning "artichoke headed" because of its artichoke-like flowerheads.