Common on calcareous soils, or those rich in bases. Reproduction Biennial forb, reproduces only by seeds and plants die after they set seed. Flowers July to October. Average fruit production is nearly 4000. Studies in coastal dune populations and in British populations have produced little evidence of seeds persisting in soil from year to year.
Germination commonly takes place in autumn.
In one study, bull thistle germination was not inhibited by dense cover, however, subsequent seedling survival was reduced. Competition Highly competitive weed. Studies have found that the spread of bull thistle is favored by trampling and soil disturbance. In Yosemite valley, the heaviest infestations were in areas that were heavily used by visitors. Digging by pocket gophers may also be important disturbance that favors the spread of bull thistle.