Much like Curt, I have solved the quack grass dilemma, or at least found a way that works for me. I started preparing my new garden areas by placing large sheets of black rubber roofing material over the entire area where the new garden will be. I also lay another piece of black rubber all the way around the future garden area. This piece
should be 4 feet or so wide. The time of year, amount of sun, temperature, etc., will determine how long the rubber needs to stay in place. It's very easy to tell if it has been long enough. Every bit of vegetation, including the quack grass, will be dead, and the earth will be bare. In my area, it generally takes 3 or 4 months in the summer. During the time it is covered, the
mice,
voles, moles,
ants, and other friendly workers are burrowing everywhere under the rubber. When I remove it, I can easily dig down 6 inches or so with my hand, as opposed to the surrounding area that you can't get a shovel in by jumping on it with both feet.
Remove the rubber from the garden area, but leave the 4 foot wide pieces that surround the garden area in place. That 4 feet is the barrier that keeps the quack grass from moving back into the garden from the surrounding area.
Immediately after removing the rubber from the garden, I cover the entire area with mulch. I use wood chips, you should be able to use whatever you like. Lay your mulch,
water the area, and plant in holes/rows in the mulch. The rubber perimeter will keep a dead zone around your garden until, or if, you decide to expand. The quack grass won't come back because it can't pass thru the rubber barrier without dying from lack of light and water, and the heat cooks it if it tries.