Minecraft wiki entry for Bamboo, associated text: When broken, any bamboo block placed or grown above it is also broken. A bamboo block drops itself as an item if a piston pushes it or moves a block into its space. When bamboo is first placed as a shoot it's not solid and can be destroyed by water flowing into it. After growing at least one block taller it transforms into another kind of bamboo block that is solid and can't be destroyed by water. To transform a bamboo shoot into a solid bamboo block place another bamboo on top of it.