It also depends somewhat on what you do with the grass from the lawnmower. If you just throw it on a landfill, as it decomposes, it too will release methane.

It also depends somewhat on what you do with the grass from the lawnmower. If you just throw it on a landfill, as it decomposes, it too will release methane. This is why many (although not nearly enough) landfills have small methane-burning power plants next to them.