When it’s in a dump it becomes so compressed that it doesn’t break down properly. It decomposes anaerobically, releasing methane, a potent greenhouse gas. Also composting is done locally whereas all the local landfills are full. So landfill waste needs to be trucked farther which requires lots of fuel, money and puts lots of wear and tear on roads. Last, composting produces fertile soil for reuse in gardens, parks and tree pits.