Did you ever notice that when you enter the woods during the fall, there is no effort being made to remove every leaf the second it hits the ground? Yet if you look around your own neighborhood, or even your own yard, fallen leaves seem like an enemy that must be eradicated. Homeowners and landscapers sally forth armed with brooms, rakes, and leafblowers to do battle with nature!
Fallen leaves are meant to be returned to the soil. Insects, isopods, millipedes, and other invertebrates shred them and eat them. Fungi and bacteria decompose the leaves into a rich organic matter known as humus. This organic matter can then be absorbed by plants, including the trees that originally produced the leaves. The plants use this organic matter to grow, and (surprise) produce more leaves! A healthy fertile soil will be rich in organic matter.
Removal of the dead leaves disrupts this cycle of soil building and renewal. I am not sure whether to laugh or cry when I see people remove all of their fallen leaves from their lawn and then apply fertilizer to replace the nutrients that were included in the fallen leaves. The same logic applies to grass clippings; they should be left on the lawn after mowing.
Current social norms dictate that homes should have a lush green lawn. Leaves allowed to pile up may smother the lawn over time before they decay. So how can the average homeowner both keep their lush green lawn and avoid raking away all the nutrients encased in their fallen leaves?
The lawnmower is your ally in this fight. Normally I advocate mowing as infrequently (and at as high of a setting) as possible, but in the fall I sometimes use my lawnmower on a daily basis. My lawnmower is set up to mulch leaves. There is no bagging mechanism or discharge chute attached; every leaf (and blade of grass) is chopped into tiny bits before falling to the ground. Some of these small bits blow away, but by mulching the leaves I am able to help accelerate the process of decomposition. More broken edges means more places for bacteria and fungi to infiltrate the leaf and fully decompose it into the humus that my lawn and I desire.
Do I mulch all of my leaves? No, those that fall in the flower gardens are allowed to decay naturally. They slowly decay over the course of time. Until they decompose they form a layer of mulch which helps to suppress weed growth. So my advise to anyone who wrings their hands and frets as soon as the leaves begin to fall... Relax and leave those leaves alone.