Safely removing Canada Thistle (Cirsium arvense (L.) Scop)

I have a raspberry patch that is 3 ft X 50 ft. i have been fighting Canadian Thistle in this patch for 2 years (this is my third). All I have been doing so far is to keep popping the tops off with a dandelion weeder. Seems like every time I pop one off, 3 grow back.

This area has 4" of wood mulch over the top of the soil, but that doesn't seem to slow it down any. I don't want to use any "nasty chemicals" on them because they are very closely intermixed with my raspberries.

I was hoping the raspberries would get dense enough that the thistle would be choked out eventually, but that doesn't seem to be happening. Instead, the thistle just seems to grow taller faster.

At this point I am spending about 30 minutes almost every morning removing thistle (and getting poked half to death between the raspberries and the thistles).

Does anyone have any ideas how to control these effectively in a organic manner?

Can you get a cardboard mulch under there?

What about boiling water?

We are also fighting thistles along the fense and everywhere else. paracelsus is right - you have to mow them down, cover with cardboard and then mulch. Never let them go to seed. They spread by long and tenacious roots too.

I've heard several times they do not like rich soil - sounds counter-intuitive, but you might try a little fertilizer or better yet compost too.

We have canadian thistle also. As much as I hate using chemicals, we've ended up spot spraying. I read in one of the articles below that if you have plants around that you don't want to kill, you can apply by hand with paintbrush or something similar. Timing is key when you apply. If you have any that have flowered, cut the tops and bag them. Our road association board is looking into alternative options such as biocontrols, but i think it is pretty pricey.

http://www.fs.fed.us/r10/spf/fhp/leaflets/thistle.htm

Here's a company in my area that sells biocontrols. They might be helpful to talk to also.

http://www.integratedweedcontrol.com/canadath.htm

Good reading upfor - thanks for the info!