Is planting on the graves forbidden?

I was told from Salafi guy that planting on the grave is forbidden as Prophet Muhammad (PBUH) did it only for himself and none of the Sahaba did it. The Hanafis, Shafi`is, and Hanbalis have all declared it to be recommended to place green stalks and the likes on the graves. If Prophet Muhammad (PBUH) did it, I wonder why the Sahaba didn't follow it (if that is true)? Can it be an innovation?