Wild apple trees originally thrived on the forest edge. The best way to recreate the forest edge for an apple tree is to place wood chips from deciduous trees around the base of the apple tree. The wood chips are digested by fungi,which in turn feed the apple tree. Apple trees love a fungal environment. If you have mushrooms growing near your apple trees, congratulations, you have created a fungal environment, for your apple trees. As a side note, when chemical fertilizers are used on an apple tree, one is creating a bacteria based environment versus a fungal environment.