Minecraft wiki entry for Birch, associated text: Birch trees require a 3×3 column of unobstructed space at least 6 blocks above the sapling to grow (7 blocks including the sapling itself). Additionally, birch trees require 5×5 layers without obstruction for the top 3 layers of its final height. No horizontal clearance is needed at the base of the tree (a sapling planted in a hole 1 block deep can still grow).