I have a problem with couch grass in my perennial beds. I've tried a lot of things (including digging up entire beds and painstakingly removing the grass roots), but this method seems to work pretty well to CONTROL (not eradicate) couch grass. You sort of "kill it with kindness." I found that if I put down a good layer of loose mulch...wood chips are ideal...over the course of a few months, especially as the lower levels of the mulch begin to decay/compost, the couch grass begins to migrate "upward" into the mulch layer and out of the soil, seeking the better nutrients and moisture in the decaying mulch. The trick is to keep the mulch moist, either with rainfall or regular watering (which is good practice for any perennial bed). Once the couch grass migrates up into the mulch layer, it's a lot easier to pull it out and I can often pull some very long lateral roots out of the ground. It's certainly not a fast solution to eradicating couch grass, but it does work well to control it and over time...years I would think...if you are dedicated about pulling the grass as it emerges, you can eventually get rid of couch grass.
