I’ve heard that “fire days” are when you can cut thistle and it won’t come back up. Is this true, and what are the days?
Thistle is a stickler, for sure. Unfortunately, the best way to rid your lawn of it is to do some serious work involving mulch to smother it — a plastic mulch for the warm-season thistle crop and shredded paper mulch for the cool-season crop. A three-inch-thick layer or more of straw will also smother it. Thistle can lie dormant for three to four years, so you have to be diligent and consistent at least that long. In addition to mulching, plow the garden deeply in the fall. Don’t rototil at anytime if you can help it; this can spread the plant further. Cut thistle at its base at the onset of flowering, whenever you see it.