Mulching is nature’s recycling system. Nature spreads thin layers of organic materials evenly over the surface of the soil. Year after year, season upon season, leaves and blades of grass mature, die, and fall to the ground. Soil organisms begin the process of decomposition. First molds, then bacteria, later earthworms and beetles all come to return organic matter back to the soil from which it came. In this process of natural mulching, topsoil is gradually created over time. Rich layers of humus—decomposed organic matter in the soil—are formed that give the soil its dark color and good rich-earth smell.

You may find it surprising that the first bit of advice is to avoid composting as much as possible by learning how to mulch various organic materials. Mulching simply refers to any technique where organic matter is spread in thin layers on the surface of the ground and left to decompose naturally so that soil organisms can convert it to humus. Decorative bark layered around shrubbery is a popular mulch. Wood chips are often spread around trees and landscaping to hold moisture. Grass clippings, leaves, and compost can be placed around garden vegetables, flowers, and in soil beds to keep down weeds.

Leaving blades of grass on the lawn is the most common mulching technique. All mulches help retain water in the soil. Mulch keeps the soil cool in the summer and warm in the winter. In fact, mulch is a form of drought insurance. Mulching is the easiest way to avoid generating organic waste in the first place. Leaving grass clippings on the lawn is the simplest type of mulching. But mulching is not practical for all residents and homes, and not all yard trimmings are easy to use as mulches.

Leaves
Leaves can also be mulched. Leaves left on the ground over the winter will not harm the grass, which goes dormant in most climates. In the North, winter puts leaves through a “freeze thaw” cycle that helps soften them for decomposition. Winter snow and Spring rains provide needed moisture for the subsequent breakdown. Layers should not be more than six inches thick.  Chopping, shredding, or mowing the leaves before using them as mulch can assist leaf mulching. 

Earthworms: The Mulching Assistant
Earthworms are the ultimate mulch specialists. The common nightcrawler, lumbricus terrestris, is a seasoned mulch hunter. Following every rain, or in the cool, moist mornings, hundreds of earthworms come to the surface to feed. These "mulch munchers" grab leaves, blades of grass, and other bits of organic matter and "tow" them back to their burrows. Deep under the soil, these worms store organic matter, excrete digestive juices to help them decompose the matter, and feast upon the resultant compost at a later date.

The worm devours the decomposed mulch and deposits the humus both in the burrow and on the surface as earthworm castings. Since the worms continually excavate and turn the soil, the humus layer remains near the root zone while the surface is continually cleared of debris. Earthworms will maintain a population level equal to the available feed or mulch. They keep the soil loose, aerated, and well drained. Working in harmony with other organisms, earthworms turn under the seasonal mulch layers, "vermicompost" it, and convert it to available plant nutrients.

Passive Composting
If yard trimmings are left to accumulate in a pile for extended periods of time, it is no longer a mulch and it begins to enter the realm of composting. The simplest compost piles are increasingly larger mounds of organic trimmings that are left to sit and rot over time. For some people, these "passive-compost" piles are largely a backyard disposal system. Even the most passive composter, the truly

lazy organics recycler, eventually finds themselves with "compost" and will put it to use growing plants. Once they do, they inevitably see the benefits of compost in soil texture, water holding capacity, and plant growth. Many of these passive-composting individuals gradually become active composters as they desire more compost or compost more quickly.

But most people will never put more effort into their piles than is absolutely necessary. Getting a finished compost in three months instead of three years is apparently not worth the effort. Passive composters are by far in the majority. Studies have shown that most householders practice the “let it sit” sort of passive pile. Passive piles are the “layer in the bin” systems recommended by most composting books. The best thing about passive piles is that they work! I find it amazing that compost happens even if we do little to assist the process.

If you wish to start composting and are not looking to do a lot of work and wish to avoid the effort of mixing or turning an active compost pile, then just start! That’s right, start composting today. There is little more to passive composting than making a pile somewhere in the yard. Purchase a bin, an enclosed plastic one if possible, and let your pile lie. That is all there is to passive composting. Rainfall, earthworms, and nature can be left to do their work, and given time, will decompose virtually any organic material fairly well. Passive composting piles can take many forms. Some are piles in the corner, most use a bin of some sort, and others use mounds of organic materials as a means of filling in low areas.

Once started, keep in mind that there is some wisdom in the practice of just letting sleeping piles lie. Moistened passive compost piles can be quite odorous if disturbed before their time. However, if the pile is never turned, there is little need to worry about odor. It is primarily the need for space, the desire to concentrate organic materials in a controlled area, and a need to process materials quickly in a nuisance-free manner that leads people to build active compost piles that require regular tending.

People should feel encouraged to be creative and to experiment within the bounds of neighborly cooperation. Some individuals have made satisfactory, although occasionally odorous, compost simply by letting grass clippings sit in sealed plastic bags for a season in the sun. One master gardener I know uses a three-pile system that he turns only once a year, producing rich humus in the third year. Most plastic bins have a door at the bottom where dark crumbly compost can be removed at the same rate that fresh table scraps and yard trimmings are placed on the top. 

Mulching Versus Composting
Active composting has an advantage over mulching or passive piles because diseases and weed seeds are progressively destroyed when a compost pile is sustained at temperatures of at least 131°F for extended periods of time. Composting "cooks" weed seeds with high temperatures, whereas mulches help smother weeds. Active composting has the benefit of rapidly decomposing organic matter, where some mulching processes can take several years. However, thin layers of grass left on the lawn decompose at least as rapidly as they would in the compost pile.

Mulching is an excellent example of a "keep it simple" program. Soil organisms are perfectly capable of decomposing leaves and grass clippings without the high "thermophilic" temperatures of compost piles. After all, nature doesn’t gather thin layers of organic material into a concentrated pile, water the layers, turn and aerate the heap, and later spread the finished compost back into thin layers. Thin layers are often best left as thin layers. The roots of plants care little whether the organic matter in the soil was produced from the best hot compost piles or from years of accumulated thin layers. Organic matter is organic matter, and the soil benefits regardless of the technique of decomposition.