John Boyd , Extension Weed Scientist Introduction Thistles attract a lot of attention because, in addition to competing with desirable forages for light, water and nutrients, their spines cause grazing animals to give them a wide berth. Life Cycle In Arkansas, musk and other thistles usually behave as biennials or winter annuals and rarely as a summer annual. The typical scenario is germination followed by the formation of a low growing rosette in the first growing season. The thistle overwinters in the rosette stage and begins stem elongation the next spring. The flowering process begins in mid-April with flower heads produced from May to June.
Plants die after seed is produced.
Several seed heads, capable of producing up to 10,000 seeds per head, may be produced on each stalk. Not all of these seeds are viable. M.K. McCarty, the dean of thistle researchers, found that plants allowed to mature produced around 3,500 good quality seeds per plant. Seeds may remain viable in the soil for as long as five years. Seed Dispersal Wind is the primary means of seed dispersal in thistles.