Minecraft wiki entry for Pumpkin_and_melon_farming, associated text: The attempt to grow a fruit happens when the mature stem would grow again (to "phase 9") and is not already adjacent to an instance of its fruit. First one of the four sides is chosen. If this space is suitable (empty with dirt, grass, podzol, farmland, or coarse dirt beneath) the fruit is created. Bone meal does not force fruit production.