In the back woods of my house I have notice sveral white Birch trees. Some as very big and some are small, 6 ft high and the trunk is about 1 inch. I am considering replanting a few of them in my front yard. What I am tring to figure out is how big of a root ball should I expect from the trees. If a start digging at the point of the where most of the branches end the root ball would only be 6 inches out from the trunk on each side. If that is correct, how deep should I have to dig?