I have no real technical analysis to add to John Metcalfe's "make the rubble bounce" takedown: weight, watering, safety....
But the fact that any number of media outlets have picked up this notion, roughly similar in realism to the doodles of car-top lasers or backyard rocket launchers found in the notebooks of bored kids in class across our great land, says something.
One thing it says is "reporters are lazy", which you know, because you are lazy, and you would be even if you were a reporter.
The other thing it says is "we're doomed".
There are no good answers out there. We face serious, genuine environmental problems, and we have no idea of what to do about them. Reporters jump on things like planting sedum on top of buses because there really isn't anything else to put in their stories.