If someone told you the Sanitation Department picked up two or three dollars from your curb every Monday, you would want to know more about it. Every black plastic bag of grass clippings you leave for them to take contains the equivalent of two or three dollars' worth of slow-release fertilizer you could have left on your lawn. The grass clippings you are now placing at the side of the street probably represent the largest effort for the least return of all the tasks you perform as a homeowner.
Several myths are associated with why clippings are removed from the lawn, none of which are valid.
Properly mown grass clippings are pieces of leaf blades that contain three to five percent nitrogen. 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.