Getting rid of couch

A lot of us use the glyphosphate ones like Roundup. It's relatively organic though some would disagree. But when it comes to getting the job done or struggling with it, you might have to ease up on any strict organic principles.
Best time to use Roundup is soon as you see them emerging. I make the solution a bit stronger than recommended as couch is really tough stuff.

Me too - glyphosate is effective and you can plant quite quickly after using it although the trick is to spray as it's growing and allow a couple of weeks for it to be drawn to the roots and really kill the plant.

With bindweed, which can get out of control as well, pop some sticks in by it, train it up the stick then spray or paint the weed killer onto the leaves. This will ensure it is distributed throughout the root system.

I much preferred Amicide - more expensive but very safe. No longer available as the manufacturers refused to kill dogs to prove it to the EU see the entry in my diary and read the comments Ammonium Sulphamate Banned

Am going to have to resort to glyphosate this year. Part of the plot has had black plastic/carpet on for 1 and part for 2 years, and yes it has killed the couch grass, but the roots are still there, they're huge!!! But very easy to dig out.