hi K.,
I have been and organic gardener for nearly 20 years, and I understand your frustration with grass growing in your garden. You don't say what kind of garden, so I'll assume this is a veggie garden rather than a flower garden. There are 2 main ways to get rid of grass: mechanically or chemically. Mechanically you can till, dig, plow, or otherwise disrupt the roots of the grass so it does not come back. Chemically you can use really yucky stuff that you wouldn't want to grow food with anymore, or you could use vinegar or very hot water. Using a vinegar solution (about 1 part vinegar to 4 parts water) is likely going to be more successful than hot water. To help this process after applying the vinegar, you can cover the area with layers of newspapers and/or black plastic to finish off the grass. Then keep the area covered until you are ready to prepare your soil for next spring planting. I hope this is helpful.