You might want to look into doing something to aid the drainage situation. I've also read that Avon's Skin-So-Soft helps.
Other ideas. At this first site, it was recommended by a friend.
You might also want to read this about plants that really don't work.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.