Don't know about fertilizer but when you put up the deer fencing you might want to put something around the lower foot or so of the trunks to keep them from being gnawed on this winter. I planted 3 apple trees primarily for the deer in a few years and put up fencing made from old cattle panels cut into thirds but neglected to guard the lower trunks. After the snow melted I checked on them and mice or voles had evidently tunneled under the snow and ringed all 3 from the surface of the ground up to about 2 inches high.
