I have a pin oak about a foot across at the stump. They let the place go and thier was some kind of bushes that was growing next to it that i cut down 3 big trailer loads to get it gone. They were on one side in a group. I have tryed several things to kill it and it keeps growing back and the ground is about a foot higher were they grow. I want dig up the roots and to level the ground. How deep can i go without hurting the Oak tree? I wish i would have pulled them now.