If you wish to grow a Fuji apple tree for its fruit, you'll need to plant at least one other apple tree nearby for the sake of pollination. Typically, the mature spread of a Fuji apple tree can reach anywhere from 15 to 25 feet. Based on that dimension, you should provide about 20 feet or more of spacing between your apple trees. Such spacing will allow the trees to spread strong branches that are easier to harvest from.