You’ve probably seen that tall spiny plant with purple flowers along the roadside. Sometimes the flowers are yellow. It’s called bull thistle and related to the artichoke. Playing ball in a pasture field teaches kids to learn to identify this one in a hurry. Fall or step on it once and you’ll pay more attention the next time.
True bull thistle (Cirsium vulgare) is a biennial. It produces basal rosettes of leaves the first year along with a thick taproot. The second season it sometimes attains heights of six feet. Despite the diminutive stature of the first year foliage, spines at midribs and tips of leaf lobes are still just as aggressive as older specimens. The yellow flowered type (Cirsium horridulum), sometimes called yellow thistle or horrid thistle is an annual. When you look at the spines you can see where the horridulum came from.
These spiny menaces grow best in sunny areas and thrive in most types of soil. Thistles are a problem in overgrazed pastures, because seeds take advantage of any available bare soil. Bull thistle can be problematic on forest clear cuts too. Plants grow fast and can shade out young tree seedlings. Seeds can remain dormant but still viable for several years.
Fortunately, the only reproduction is by seed. There are no tubers, rhizomes or other vegetative structures. However, the seed is prolific and gets spread by wind, much like dandelions. Sometimes huge clouds of thistledown spread seeds great distances.
This plant can be quite invasive and is considered a noxious weed in most states. An exotic species, bull thistle is originally from Eurasia. Flowers emerge in summer and it’s best not to let them mature unless your goal is to attract finches. They love the seed.
Controlling bull thistle by non-chemical means usually involves some type of physical protection. I’ve hand weeded them, but I always use welder’s gloves and wear long pants and long sleeves. Even then it can be a struggle because the roots are often large. Once plants flower they are easier to pull, but you’re playing with fire if the seed is mature.
On larger areas it can be kept under control by mowing it regularly so it can’t set seed. That still won’t solve your problems if you or your children like to walk barefooted. Numerous herbicides will kill it also, but on pastures they also can damage desirable species. In lawns they are rarely a problem. Always read the label thoroughly.
Believe it or not bull thistle can be a valuable survival food. In their first year roots are edible and when cooked they strongly resemble Jerusalem artichoke. If you’re inclined to try them, take a shovel and cut the tops off before digging the roots. Once roots reach their second year they become too woody to eat.
According to many sources, young leaves make a fair cooked green. The spikiness gets tempered by cooking, but collecting them would not be a pleasant experience. Some even recommend using young leaves in salads. That almost seems like joke to me. I’ve never consumed bull thistle foliage raw or cooked, but then again I’ve never been starving to death either.
Ted Manzer teaches agriculture at Northeastern High School.