Lawnscraper

But it wouldn't have those crappy little sprouts. First, take a skyscraper and make horizontal trenches that are angled down and into the building about three centimetres deep and three centimetres tall all across the concrete all the way up (except for windows, obviously) three centimetres apart. fill all the trenches with a little plant food and cut strips of sod to stuff in there as well. use those window washing rigs if necessary. result: a vertical lawn on the sides of an office building. It could even have little sweat hoses running up and down the building to prevent the grass from dying out.

At this point many of you are probably wondering "well, it's neat and all, but why?" beleive it or not, I have a reason. Air purity. More plants in a downtown core would help filter pollutants from the air, But trees and lawns don't always fit on narrow streets, and lots of them die from being poisoned by the air. If there were enough plants, this wouldn't happen, but there still isn't enough room unless you think vertically. plus, green office buildings would look cool. you could also design the trenches to spell out company logos and stuff. You could even paint the grass for temporary advertising. I'd include something about the greenhouse effect, but a bunch of sod just isn't gonna fix that.