I did the same as you for years and could not get totally rid of quack grass as any little itty bitty roots remaining in the soil will grow. I finally decided to spray with fusillade II after folks on the AHS daylily robin recommended the product. This works well for me I do have to repeat every couple of years as quack grass will creep in from somewhere. I spray where the quack grass is actively growing then wait for a week or so while the grass dies off, if you spray when you notice the grass it will grow back less and less. I am not sure where you are located but here in my climate this stuff works versus spending a lot of time trying to dig it out and failing, sometimes a person needs help against such an invasive grass. By the way it has not harmed my flower plants and when needed I just spray not trying to protect other plants as the grass gets to intertwined.
One more thing there are butterflies, dragonflies, bees, toads and lots of birds enjoying my garden. I would rather have time to enjoy my garden instead of endlessly trying to dig out quack grass only to see it growing again where I just thought I had removed it all.
