We have also been plagued by thistle. Has been an ongoing battle for the 20 years we have lived on this property.

I can't comment on the effectiveness of clear plastic as a 'thistle killer'. Have never tried it. Seems like a huge (and perhaps futile?) undertaking when large areas are involved.

Cutting and/or mowing the area frequently will eventually stunt or slow its growth. This method is not always possible, depending on the terrain involved.

If you are not opposed to using chemicals as a control, a broad leaf weed killer, labeled for thistle will work. Must be used according to the label and used more than once. A one-time application will not kill/control thistle. If almost no other vegetation exists in an area except thistle...reseeding heavily with grasses after the broad-leaf herbicide will help build turf over time and be a deterrent to new thistle coming in from the dormant seed.

An area of well established thistle that has been there for years will be an ongoing problem. It has reseeded for years and the seed will remain dormant forever...or so it seems. Each time the sod is disturbed a huge new batch will appear and will need to be attacked with vigor.

Good luck on your battle.
Jan

I always get a chuckle out of the thistles that are grown as ornamentals! After fighting Musk Thistles on my parents farm all the years I was growing up, I just can't picture myself planting any kind of thistle on purpose.

I remember my dad once saying that the first time he saw one of them growing along our lane, he thought it had the prettiest flower. Then he followed up with "if I'd known then what I know now, I'd have got the hoe and chopped the sucker down!"

He used to give my sisters and I a penny apiece for chopping them. In pastures where they were tiny, the money was good. In other places, we sure did work for every one of those pennies!

Here is a link that might be useful: Musk Thistles

I heard a poem on MPR once that said you can never get rid of thistle, like you can never get rid of true love, or something like that.
We have thistle growing in a corner of our vegetable garden that I dig out at about 1.5 feet. I know there are runners deeper than that, but I do this just to get rid of some for the summer.
We never had thistle or nettle in our yard until we got a load of black dirt from a local peat supplier 15 years ago.