Bull thistle

Image by: James Altland, USDA-ARS
Bull thistle flower heads are pink to purple, and approximately 1 inch tall and wide.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Bull thistle is a biennial forming a rosette during the first year of growth.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
At maturity, plants grow 2 to 5 feet tall and wide.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Bull thistle foliage is dark green, pubescent, deeply lobed, with stiff spines at the tips.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
By late summer, seed heads mature and begin seed dispersal.
Image by: James Altland, USDA-ARS
Cirsium vulgare
Family: 
Asteraceae
Life cycle: 
Biennial
Habit: 
Bull thistle is a biennial that forms a rosette the first year. Rosettes can grow up to 3 feet across. Erect foliage and flower stems are formed the second year. Mature plants are branched and often grow 2 to 5 feet tall. Dark bluish-green foliage is pinnately lobed with coarse hairs covering the top surface, woolly hairs covering the underside. Long, sharp spines grow at the mid rib and the end of each lobe.
Flowers: 
Flowers are bright pink and larger than Canada thistle. Each stem is topped with a 1-2 inch, gumdrop shaped flower. Flower bracts have spines. In contrast, Canada thistle’s flower bracts do not have spines. Bull thistle typically flowers June through September.
Favorable environments: 
Field
Favorable environment notes: 
Bull thistle is adaptable to many environmental conditions from dry to moist areas. It prefers open sunny areas commonly found in pastures, logged areas, along road sides and trails.
Dissemination: 
Bull thistle reproduces only by seed. It does not reproduce vegetatively or have rhizomes. Each seed is topped with a cottony plume which makes them easily dispersed by the wind. Germination can occur in the fall and in the spring. Seeds are short lived while on the soil surface, but can persist buried in the soil for years.
Of interest: 
Bull thistle is a classified as a noxious weed in Oregon and Washington. Regular cultivation can greatly reduce numbers of this weed in agricultural areas.