Mulching: Nature’s Composting Secret

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, especially grass clippings. 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. Brush must be chipped before it can be used as a mulch, and few residents own brush chippers. Many communities operate municipal wood trimmings collection and chipping programs with the wood mulch used in public areas such as parks and roadways. There is probably a Christmas tree mulching program in your area.

How to Mulch Grass Clippings
The easiest way to start mulching is to take the grass catcher off the lawn mower. This tip is so important that it bears repeating. Take the catcher off your mower! Your mower service shop should be able to put a trap door over the discharge end if your mower does not already have one. For conventional side discharge mowers without a trap door, mulching may require a bit of raking following mowing to break up the little rows of clippings. To avoid raking the entire lawn, mow from the outer edge in ever-smaller circles toward the center, making sure that the side discharge mower is “walking” or blowing the grass clippings ever closer to the central point. In this manner, clippings are chopped several times and most fall between the blades as mulch. The few that are left near the center can easily be raked and placed into the compost bin or spread in the garden.

Mulching mowers have become quite popular in recent years and dealers proudly display their new features. Advertising campaigns are helping convert homeowners to these new “zero discharge” mowers. Mulching mowers are designed differently from conventional mowers with closed trap doors. The first difference is, of course, the lack of a discharge point and a catcher. The second is the horsepower rating, since mulching mowers require more horsepower to cut and re-cut the grass. The special blade not only cuts, it also acts as a vacuum and fan that circulates the clippings back to the blade for additional pulverizing. The air pressure then forces the chopped clippings downward into the lawn. Even replacing your regular cutting blade with a mulching blade can turn a regular mower into a better mulching mower.

Mulching mowers require a lawn that is not overly wet and has not been left too long between cuttings. The height of the grass should be somewhat higher than typical settings for bagging mowers and the lawn is best cut when the grass is one third higher than the height of the blade. For the average lawn, if the grass is left at two inches following mowing, the grass would be cut when it reaches three inches. While the new system takes some getting used to, user satisfaction is running near 100% for those who have made the switch. The lawn must be mowed more often than with conventional mowers, but the time actually spent in the yard is less because there is no need to continually stop and empty the catcher. Mulching mowers should be used every five to six days instead of every week.

Cutting grass higher with only one third the blade height is easier and faster than cutting overgrown grass. Fertilizing can be decreased since grass clippings contain 4% nitrogen and act like a time release fertilizer when they are returned regularly to the soil. Grass clippings return to the soil to form organic humus that helps hold water while keeping the soil loose and aerated.

The Economics of Mulching
Mulching can be viewed as an economic issue. Leaving yard trimmings at home is a means whereby the homeowner can stop paying for the plastic bags, the trash hauler, and the waste disposal operation. Mulching means lower taxes.

With mulching and composting, householders can manufacture their own topsoil and soil amendments. At three dollars per cubic foot bag at the garden center, one cubic yard of mulched yard trimmings represents a saving of over $80. If one cubic yard of compost can be blended to make ten cubic yards of topsoil, then a yard of compost can equal one truckload of black dirt worth at least $100.

In addition to the cost benefits, you also reduce your dependence on landfills while experiencing first-hand the satisfaction of conserving natural resources. Like those who enjoy feeding wild birds, mulching is a means of feeding the soil ecosystem and the associated plants, trees, and landscape that give us pleasure while beautifying our homes.

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.

Leaves can be gathered and placed into wooded areas for mulching. They should be spread evenly, never more than six or eight inches deep. Random and unattended piles several feet in height are neither a mulch nor a compost. Take the time to spread your leaves evenly so that they can decompose properly. If you have no natural undergrowth areas on your property, be sure to ask permission of any adjacent landowners to spread leaves in their woodlands before using it as your disposal site. At no time should you use vacant lots, public parks, ditches, rural areas or piles over the fence as dump sites. Many communities have a program whereby local farmers allow householders to bring their leaves out to the farm for spreading in the fields. Mulching is the beneficial use of organic matter that also happens to solve a disposal problem. Dumping leaves is a public nuisance and is often punishable by fines.

Chopping, shredding, or mowing the leaves before using them as mulch can assist leaf mulching. Care must be exercised when handling dangerous chopping equipment. Make sure that your machine or mower is rated to handle leaves and that all necessary safety precautions are used. Safety glasses, gloves, and heavy clothing are wise items to wear during all pulverizing operations.

Leaves that are placed in large piles in the fall tend to insulate themselves and shed water, delaying decomposition. The following Spring the leaves look much like they did months before. If leaves are gathered in the Fall, they should be moistened several times, layer by layer, to aid decomposition. Soil wetting agents sold at garden centers or through organic detergent retailers assist in the process of getting dry leaves to take on moisture. If possible, spread leaves over the garden, in flowerbeds or wherever there is open soil. The three keys to getting leaves to decompose are watering, moisturizing, and wetting. And then they should be watered again.

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.

Many gardeners have had success introducing redworms such as eisenia fetida (the common red or “brandling” worm) or lumbricus rubellus (the red wriggler or so-called “hybrid” redworm) to their lawns and gardens. Redworms devour the humus layer of the soil voraciously, quickly turning mulch into castings. Native to temperate river deltas, redworms require a moist, well drained, rich topsoil with plenty of mulch and organic matter. They will not burrow to escape the frost and drought, however, as do their nightcrawler cousins. They will only live for a few months in the lawn or garden in most climates. Redworms may have to be replenished annually in the humus-enriched or mulched garden and lawn.

Always remember that redworms cannot make a poor soil good, only a good soil better. The aeration and mulching benefits provided by redworms is hundreds of times that of the less active nightcrawler. A few dozen redworms purchased at the bait store or a few thousand ordered through the mail from garden catalogs are often sufficient to get started. They breed like crazy and will quickly increase their population to handle any volume of household organics.

Many people add redworms to their compost pile and let them quickly eat the table scraps and other organics stirred into the top layer. Redworms will enable the pile to decompose much more quickly than letting it sit passively. The best thing about earthworms is that they do the mixing and aerating all by themselves, living on the decomposing compost and the regular addition of discarded fruits and vegetables. You don’t have to turn the pile to get it to cure when you let redworms do the work for you. But redworms should not be used if you are making active batches of compost. The heat will cook them or drive them to the edge of the pile, often to their death. If using active composting techniques, wait until the pile has cooled before adding redworms.

Many people use redworms year-round right inside the house to take care of their table scraps and a limited amount of shredded paper products. In the basement or under the sink, they keep them in plastic bins that are less than one cubic foot in size. As long as they are kept warm, moist and protected from light, one small worm bin per person will consume the daily production of vegetable and fruit discards along with the coffee grounds, filter and all, on a year-round basis.

Worm farmers need to periodically remove the rich earthworm digested compost, called “worm castings,” as worms do not like living in their own manure for more than a few months. Worm castings, however, are worth the effort of indoor worm ranching. This “super compost” is the best ingredient in potting soils and is valued above all other compost products. Experienced gardeners will point to the soil worms in the garden and the redworms in the worm bins as the secret to their exceptional yields.

Composting

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. Compost produced from passive piles is just as beneficial for the soil as is compost from active piles.

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.

© 2000, Jim McNelly