Tilling doesn’t do an effective job of pulling spreading or expansive weeds, although it makes uproot some. It’s best to pull as many weeds as you can before tilling so the roots don’t get caught up in the tines and prevent them from reaching the soil. It’s also best to pull any grass you have before tilling. While you can simply use an herbicide to kill the grass, once you turn it over, the grass could take root again and begin to grow in your garden..