Years ago, I went and got a pickup load of the free city compost. Worst thing I ever did. Introduced dozens of bad weeds, but the worst was thistles.
We have tried everything on them. Round-up, Weed-Be-Gone. They come right back.
We tried both at once, at the suggestion of the local nursery. Came right back.
We tried gasoline. BACK!
We tried boiling water. Took longer to come back.
We tried building a fire on top. Took longer, but BACK!
We tried solarizing with plastic. They travel to the edge, then BACK!
The only thing that worked was a large pile of horse manure. But it was five more years before we could use this chunk of land again.
There truly must be something that works. Our next plan is to douse some with lighter fluid, then set em on fire.
But I know what will happen. BACK!