After several years of daily thistle removal from my allotment I am considering clearing it off now (the thistles have prevented most other things from growing this year) and covering it in black plastic over winter in the hope that we will have less thistles to live with next year.
There are a lot of white thistle seeds blowing into our garden at the moment because there is a neglected garden about 50 yards away which had been completely taken over by thistles.
Last spring I tried to remove all the thistle root from the allotment, but this does not seem to have worked. I don't really want to use chemicals in the allotment to fix this problem, I think that if you are putting chemical weed killer on there then there is little point in growing your own vegetables.
I have had limited success with pouring boiling water over them, but they do seem to return within a few weeks of doing this.