Minecraft wiki entry for Sapling, associated text: Tree saplings have two growth stages (with no visible difference between them) before growing into trees. When a tree is to be grown, a height is chosen and then the ground and space are checked; if the ground is bad or there is not space for the chosen height, the tree does not grow. Bone meal can be used to speed up the growth of the sapling, even to grow the tree without sufficient light.