I have a large tree in my back yard, no idea what it is, branches used to cover the entire back yard. I just trimmed it so I could get more sunlight in the back yard so the grass would grow, and to keep it from beating up my house. So far it hasn't grown, so I would like to prep my soil and plant new sod/turf. From what I've read so far, to do it right, I will have to till the soil to a depth of about 4-6 inches. I don't want to spend the $$ on the new grass just to watch it slowly die. The large tree in question has roots running all over the yard. The question is, how far away from the base of the tree do I need to be to make sure I don't kill it.