Why should lawn clippings be left on the grass after mowing?
The clippings are a valuable source of nutrients for the lawn. Young, short clippings decompose quickly. They give off nitrogen, potassium, and phosphorous, which act as natural fertilizers. Furthermore, landfill space is saved when clippings are left on the lawn instead of being placed in the trash. Sources: 50 Simple Things You Can Do to Save the Earth, pp. 42-43; Vengris, Jonas. Lawns, 3rd ed., p. 123.
