The bug
Bone meal is completely useless on kelp, but the item still goes to waste and nothing happens (although the particles still appear and it still makes seagrass grow if you do it near the floor).
Comments 8
@unknown, don't take the Wiki as reference. The Wiki is describing the game as is, including all bugs.
This works as intended.
Acc. to the Minecraft Wiki bone meal has no effect on kelp.
In the engish version of the wiki is no entry for this behavior but on the german page you find some information about this.