Do you mean Elytrigia repens, Common Couch? I'm afraid it will grow over and through anything you plant. See here for advice: https://www.rhs.org.uk/advice/profile?PID=283

Sadly you have to get out every last bit of root, which can mean digging up any perennials its growing through and trying to unthread it, then forking over as deep as is practicable.. If you have space you might try clearing one area at a time,& moving your plants somewhere else for a few months. Even then you'll probably get the odd bit growing back but constant vigilance will sort that if you've got it out of all the plant roots before replanting.

Scotch Grass (Urochloa mutica) or Scotch Moss (Sagina subulata), Susana?