These succulent morsels of organic matter are rapidly decomposed by soil-dwelling microorganisms and disappear within 10 days. The key not to cause thatch is to mow the grass frequently enough at the proper height never to remove more than one-third of the canopy. Each grass responds best to a different mowing height. When the grass is growing well, returning clippings to the lawn has no effect on most diseases. It takes more fertilizer to decompose the clippings.
Clippings add up to three pounds of nitrogen per thousand square feet of lawn.
The clippings are a slow-release source of everything the turf needs to grow. Although grass clippings disappear quickly when returned to the sod or placed in a compost heap, clippings placed within a plastic bag and buried in a landfill are still identifiable after 10 years. The anaerobic conditions within a landfill prevent microbial action. It is easier and cheaper to put clippings by the roadside than to do anything else with them. Additionally, landfills are filling up and many cities are considering not picking up clippings or charging a fee for the service.