PTIONS O bull thistle by hand before the flowers the before hand by thistle bull Copious production of production Copious seeds. wind-dispersed 10 years. least be at to Seed thought longevity High germination success rate. from removed unless taproot from Resprouts crown. below Pull yourselfopen. spare To spines, the the on step side one to over leans thistle the so that stem bend pull down to it. you before If the ground is hard, and then with a pick the soil loosen of as much pull up as possible. the taproot bud the beyond are that heads flower any Clip stage if population size is small. REATMENT u u u u T u WEED WORKERS’ HANDBOOK WEED WORKERS’ ACTORS F Bull erect thistle’s spiny stems and spreading ESCRIPTION EY EPRODUCTION Spines necessitate the use of plant. heavy this on leather working when gloves MPACT K u Bull thistle can establish in grassland and scrub in grassland can establish thistle Bull habitats,quickly colonizing open patches.It also of value the reduces lands. forage I R Bull thistle reproduces solely by seed. It bolts year, second in the generally and flowers from September. to June terminal, are Flowers 1.5–2 inches across, and rose-colored to magenta or purple. base of The is cone-shaped flowers the with spines. green covered and densely Light brown, from release ripe for seeds are oblong toJuly October. Each plant produces seed only dying, before once thousands can produce but of seeds. drop most that suggests research although wind-dispersed, seeds are The within a few feet of the parent plant. Seeds ger- and fall. in spring minate branches reach 2–5 feet.The reach branches of surface upper the with short,stiff is grayish-green leaves hairs; the gray. a woolly are undersides are The leaves alternate, stout, appear- a winged and have ance, yellow lobes and a long with pointed a rosette tip. the at spine produces thistle Bull of year. first in the A fleshy leaves low-growing taproot can grow up to 30 inches long. D on found commonly is a biennial thistle Bull recently disturbed sites and forest clearings, but it also invades native grasslands. It thrives on moisture. Also known as spear thistle spear as known Also Cirsium vulgare (Asteraceae) Family Sunflower BULL THISTLE BULL

PERENNIALS & BIENNIALS 74 u Cut the stems to at least 1–2 inches below FOLLOW-UP ground with a sharp-edged shovel before the Not all bull thistles flower in the second year, so flowers bloom. Remove flower heads when follow up for several years to catch those plants feasible, i.e., in small populations. The plant still in the rosette stage. Dig up rosettes each may continue resprouting if the root is left in year or chop out 1–2 inches below ground. the ground, so follow-up is important. Replanting the area with native species will dis- u Mow after the thistles have bolted but before courage bull thistle, which thrives more on they flower. A second mowing one month open,exposed sites with little competition from later is usually necessary.Thistles must be cut other species. There is also evidence to suggest close to the ground. Yosemite National Park that bull thistle does not tolerate deep shade, so has had some success using this technique. you might have success using a weed fabric bar- rier in dense patches as a follow-up treatment. DISPOSAL Clean equipment before leaving the infested site The stems can be left to decompose on-site.Any to prevent the spread of viable seed. clipped flower heads should be removed (and bagged, if plants are on the cusp of developing INTERESTING FACTS seed),as thistle flowers can mature and produce Bull thistle is native to Europe, western Asia, and viable seed even after being cut off the stem. North Africa, and reached the United States as a crop seed contaminant during the colonial era. The taproots at the rosette stage are edible if cooked.

Notes PERENNIALS & BIENNIALS

THE PLANTS: HOW TO REMOVE BAY AREA WEEDS 75