Bull Thistle Weed in Florida

Identification

• Because it is a weed, bull thistle does not have assigned U.S. Department of Agriculture plant hardiness zones. However, it is native to Europe, Asia and Africa, grows freely in most parts of the United States, and is now found on every continent except Antarctica. It can grow up to 6 feet tall, with spine-tipped leaves and hairy stems. It is exceptionally prolific, producing up to 400 flowers per plant, each containing up to 300 seeds. It generally inhabits already disturbed areas, such as pastureland, rangelands, roadsides, ditches and fence lines.

Life Cycle in Florida

• The bull thistle is a biennial, which means its life cycle takes two years to complete. In the first year of growth, the thistle looks like a rosette, growing close to the ground with a long taproot and a radial leaf pattern. It forms flower stems in its second year, sending up stalks, flowering, seeding and dying. In Florida, the rosette stage of growth usually occurs over the winter months. Then bolting, or stalk formation, takes place between January and July, while flowering occurs from April through August.

Control

• The best way to remove bull thistle from your garden is to pull it by hand. Especially if you are living with young children or pets, you shouldn’t use chemical control unless you absolutely have to. Instead, remove the plants in spring or summer by cutting them off below the soil line. You can also mow them, but will have to do so over and over again before they finally stop resprouting. Although herbicides should be applied as a last resort, several common pasture herbicides will work when applied to the plant in the rosette stage. After bolting, however, these are not nearly as effective. Therefore, if you are going to use herbicides, you should do so during the winter months in Florida.

Discouraging Return

• Because bull thistle sets so many seeds per year and per plant, they are very persistent. Time your removal in the spring or early summer, after plants have appeared but before they have bloomed. If you do try to remove them once they’ve flowered, be sure to do so before the flowers dry up and set seed; pulling them up or mowing them after that will only scatter seed more widely. Moreover, mowing them before they have produced their flower stalks will have no effect, so you must wait until those form during their second year of growth.

Precautions

• Bull thistle has very sharp spines on the ends of its leaves and will prick skin or even create puncture wounds if you aren’t careful when removing it. Always wear gloves when working with bull thistle. If you are trying to remove it from your garden, discourage children from picking its blooms and blowing the down away, which will carry seeds to new sites.