Have I opened a can of worms ? Pardon the pun. My plot is solid couch grass, so am unsure what to do. perhaps i could conduct an experiment, one bed dug, one not.
I wouldn't use this method if you have couch, my opinion is that the only way to deal with this evil is to dig it out. I use a fork rather than a spade, as it doesn't cut the rhizomes and they are far easier to pull out when they are a foot long.
It is very slow work, but I figure it is best to get right on top of it from the start. I have stripped my whole plot bare so that there are no grass paths from which it can respread.