Native to Eurasia, bull thistles were introduced to this continent during colonial times and are now found in all parts of the U.S. They can grow to 7 feet high and have spiny leaves up to 12 inches long and and pink or purple terminal flowers 3 inches long. They are biennials, developing as a flat rosette the first year, then growing tall and making flowers in their second year, blooming from June to October. Like other biennials, they have a deep, fleshy taproot. They are mostly weeds of uncultivated land, such as pastures.
Treat plants in the rosette stage if possible. Bull thistle can also be controlled by mowing or cutting all plants in the area to the ground just before blooming, preventing them from making seed.