There are some plants in the garden which are an absolute menace but at the same time spark admiration. Bindweed and green alkanet spring to mind, but couch grass is perhaps the most ingenious, as it adds camouflage to its box of tricks; when the thin green spikes appear they look relatively benign, and I often don’t register them as a threat - and this gives it the edge (at least in my garden).
If you’re chemical-free like me, there is really only one way, and consistency is the key…. Diligently and carefully weeding it out as soon as you see it will weaken it over time. Compared to bindweed, couch grass is easy to pull out, but you do need to use a widger (or something blunt and long) to chase the roots through the soil so as not to leave any remaining.
Serious combat for infestations involves removing everything from the border, thoroughly cleaning the roots of all plants and then digging over and sieving the compost with something akin to one of those plastic bread-trays. Once this is done it’s easy to spot and remove any new shoots with their rhizomes as and when they appear.
There is a school of thought, backed up by unscientific experimentation, which says that couch grass will not proliferate if buried more than six inches, so with big clumps it would be worth removing the entire ‘turf’ flipping it over and burying it in a deep trench. Your garden gets to keep all the nutrients locked in those weeds, and you get a jolly good workout. BONUS!