With the yard cleanup complete and my pile put to bed for the fall, it’s time for another favorite backyard project: Dressing my beds of perennials and the forsythia hedges with a layer of fresh wood chips.

Over the years, I’ve spread truckload after truckload of the remains of all manner of local trees and bushes, sawed into chunks and run through an industrialized chipper by a local landscaping crew, flagged down to dump their results in my driveway. If it’s not grass or patio or pavement, the ground I tend is covered by a layer of what toney landscapers call arborist mulch, where it decomposes according to its own composition and timeline.

Each fall I replenish the garden beds of perennials with a fresh layer of wood chips.

Wood chips aren’t quite as virtuous as compost, ecologically, but they do have their benefits to the backyard gardener. A four-inch layer of chips spread among my perennial beds prevents weeds from sprouting. It soaks up rainfall and slowly releases it, drastically reducing the need to water the flowers, bushes and shrubs that ring the perimeter of my property and surround the house.

A blanket of freshly minced trees gives the ground underneath the forsythia hedgerow and around the trees a uniform, manicured appearance, though for a few weeks my yard has the look of the kid with the bright new sneakers at school. And for a time, especially after it’s wetted by the first rain, a freshly spread layer of chips gives my yard a Christmasy, pine-scented smell or, when I happen upon a load made of black birch, a hint of Wrigley’s peppermint gum.

Some of my neighbors landscape their properties with store-bought mulch, made from coconut husks or nut shells or ground-up bark processed from who knows where – often dyed an unnatural shade of red or coffee brown. I prefer to get my wood chips unvarnished and for free, from nearby, and to spread them myself. I also like knowing where the chips come from, as an unsourced load of chopped-up tree or brush could introduce some blight or bug into my landscape. I’m pretty sure one year I got a nasty case of poison ivy after spreading a load of chips infused with ground-up ivy vines.

Still, the virtues of mulch are plainly evident.

“The greenness and fertility of my garden are due to vast quantities of mulch, everything from compost to salt hay to seaweed,” Eleanor Perenyi extolled in her garden classic, “Green Thoughts” (Modern Library, 1981).

“To non-organic gardeners, mulch’s primary function is to keep down weeds and conserve moisture in summer; in winter they may use [it] to keep the soil from freezing and heaving around favored perennials. But to gardeners of my persuasion, mulch is much more: It is an organic substance whose benefits extend to the soil itself, improving its structure and enriching its fertility to the point where it needs nothing else. An organically mulched vegetable garden never requires tilling, digging or hoeing, and is scarcely weeded. [Mulch] doesn’t burn or cause sudden spurts of unhealthy growth as artificial fertilizers may – it is long-term in its effects.”

Perenyi was not much in favor of wood chips, seeing them as too expensive when purchased commercially, a “staple of every corporate planting,” and low in nitrogen, requiring the addition of a fertilizer to compensate [more recent research seems to refute that, as you’ll see below]. Still, she was wholly committed to using mulches that were to her liking, “even newspapers and old carpets.”

My qualms about adding so much wood chip mulch to my grounds are assuaged by some online browsing. My search for “composting wood chips” brings me to a collection of web pages produced by Washington State University and composed by an expert I soon recognize as the modern maven of mulch, Linda Chalker-Scott.

In a 2007 newsletter produced by Master Gardener,  Chalker-Scott, who is a Ph.D. , Extension Urban Horticulturist and Associate Professor, and MasterGardener WSU editor at the Puyallup Research and Extension Center, Washington State University Puyallup, explains:

“In areas where trees are a dominant feature of the landscape, arborist wood chips represent one of the best mulch choices for trees and shrubs. A 1990 study evaluated the landscape mulch potential of 15 organic materials, including grass clippings, leaves, composts, yard wastes, bark, and wood chips. Wood chips were one of the best performers in terms of moisture retention, temperature moderation, weed control, and sustainability.

“In many urban areas, arborist wood chips are available for free, representing one of the most economically practical choices. Unlike the uniform nature of sawdust and bark mulches, wood chips include bark, wood, and often leaves. The chemical and physical diversity of these materials resists the tendency towards compaction seen in sawdust and bark. Additionally, the materials vary in their size and decomposition rate, creating a more diverse environment that is subsequently colonized by a diverse soil biota. A biologically diverse soil biota is more resistant to environmental disturbance and will in turn support a diverse and healthy plant population.

“Wood chips are considered to be slow decomposers, as their tissues are rich in lignin, suberin, tannins, and other decomposition-resistant, natural compounds. Thus, wood chips supply nutrients slowly to the system; at the same time they absorb significant amounts of water that is slowly released to the soil. It is not surprising that wood chips have been cited as superior mulches for enhanced plant productivity. Wood chips have been especially effective in helping establish trees and native plants in urban and disturbed environments. Arborist wood chips provide incredible weed control in ornamental landscapes. The mechanism(s) by which wood chips prevent weed growth are not fully understood, but probably include light reduction (preventing germination of some seeds and reducing photosynthetic ability of buried leaves), allelopathy (inhibiting seed germination), and reduced nitrogen levels at the soil-mulch interface (reducing seedling survival).

“While there are imported wood mulches available for purchase at nurseries and home improvement centers, they are not as cost-effective as locally produced wood chips, which are often free. In a society where using locally produced materials is increasingly popular as a measure of sustainability, arborist wood chips are a natural choice. Finally, the reuse of plant materials as mulches keeps them out of the landfill—a benefit with both economic and environmental attributes.”

In any event, over a season or so, the wood chips spread across the bare ground are broken down by rot and mold and earthworms to become a deep new layer of biomass that is easily tillable. True, sometimes a layer of chips gets permeated by a web-like tangle of fungus, and I’ve read that decomposing wood chips can suck available nitrogen from the soil underneath and turn the ground more acidic than some plants favor. What’s more, all that wood decomposing does add a measure of carbon dioxide to the atmosphere.

But on balance, a blanket of local, fresh-made chips spread around the walkways and untended areas saves energy all around. It lays the groundwork for healthier plants, especially when combined with compost, which I tuck around the perennials and spread across my vegetable garden and atop the densest patches of my plantings. It all makes my yard that much more of a biomass factory, though I marvel at how all that minced wood reduces to so little. I realize what I’m shoveling is mostly water and air, bound only for a moment of time into bite-size pieces of carbon.

Earlier this week, I turned out the dog for his morning relief just as a cherry-picker and a truck hauling a chipper lumbered past my driveway and stopped two houses down the street. They were there to remove a big old white pine overhanging a neighbor’s house. After watching the driver expertly back the truck and chipper up the narrow drive, I asked if he wanted to dump the chips in my driveway.

Good for him, good for me, as it’s a no-brainer to drive a truck 30 yards down the street rather than 30 minutes to some rural landfill or refuse yard. And sure enough, when I came home at the end of my work day, my driveway was covered with a pile of fresh-cut wood chips wide and deep enough to hide a car.

A freshly dumped load of wood chips nearly fills my driveway.

By now, I’ve got the process down, if not to a science, then a sport. Come Saturday, I am ready to dish. I use a wheelbarrow, a hay pitchfork with four curved tines and an old wide shovel I use to plow snow off my driveway.

I get started by leaning the wheelbarrow sideways into the pile and filling it with chips dragged from the top of the pile with the pitchfork. As the pile reduces, I use the wide-mouth shovel to scoop up from the edges. I know just how many fork-fulls or scoops it takes to fill the wheelbarrow and have a good idea of how best to wield the wheelbarrow around the garden beds to keep from burying an azalea or phlox.

Besides, wood chips – especially this load of light, bright-yellow pine, flecked with minced green – is easy to work with.

I can work my way into a dump-truck-size pile in less than a day, replenishing all of my garden beds along the way. Fill a wheelbarrow, walk it over to a garden bed, tip, then repeat. Every five loads or so I stop to rake the few piles flat across the garden beds and around the buses. It’s my exercise, a chore I relish. A moveable feast of a compost pile.

Just a few wheelbarrows left to spread among my garden beds.

Dr. Chalker-Scott’s research findings about compost can be found on a wonderfully informative website produced by the Washington State University Extension called Horticultural Myths, at http://puyallup.wsu.edu/lcs/. More of her findings may be found at The Garden Professors blog, http://gardenprofessors.com/.