Minecraft wiki entry for Tree, associated text: A sapling uproots with light level 7 or less in the sapling block itself unless it has a view of the sky that is unobstructed (except by glass or other transparent materials). The sapling must have at least 6 blocks of space above it to grow; the amount of required space varies between the different species of trees. A ceiling above sapling limits the maximum height of the tree that can grow from that sapling. However, dirt blocks and logs may not prohibit tree growth, and in some cases may be replaced as a sapling attempt to grow through them. However in Bedrock edition, logs prohibit tree growth.