Minecraft wiki entry for Bone_Meal, associated text: Using bone meal on a non-transparent block that is underwater generates seagrass on that block and surrounding blocks. Sometimes, if in a warm ocean biome, coral and coral fans may have a chance to generate as well, and in Bedrock Edition, coral (not coral fan) can be generated in any biome. In order for this to work, there must be 2 water blocks above the block the bone meal is being used on, and the lower one must be non-flowing water.