Bull Thistle at the Sweet Marsh in northeast Iowa.
Bull thistle is a widespread biennial thistle orginally from Europe and Asia, but now introduced throughout North America. Although it is intimidating in appearance and can sometimes form large infestations, this thistle is not as challenging to control as many others and is mainly a problem in hay fields and pastures. Bull thistle is also commonly found along trails, roads and vacant fields.
Branching, erect biennial, 2 to 6 feet tallBull thistle flower – click for larger image
Rosettes form in first year, flowering stems the second.
Long, sharp spines on the leaves at the midrib and the tips of the lobes.
Leaves are deeply lobed and hairy – there are coarse hairs on leaf tops, making leaf feel rough to the touch, and woolly hairs on the underside.
Leaf bases extend down onto stems and form spiny wings along the stems
Pink-magenta flower heads top each stem
Flower heads are “gumdrop” shaped and spines extend all around the base of the flower heads
Flowering June to September
Habitat and Impact
Bull thistle prefers sunny, open areas and can tolerate a wide range of conditions, from moist to dry soils, and is typically found in disturbed areas such as roadsides, trails, logged areas, vacant land, pastures and cultivated land. Overgrazed pastures are susceptible to bull thistle encroachment, and it can sometimes form dense stands that reduce productivity and stocking levels. Bull thistle may also dominate forest clear cuts and reduce growth of tree seedlings.