Nature has an aversion to bare naked soil and so do I. In natural settings in Illinois, soil is generally shaded by plants and covered by organic debris (mulch) of one kind or another. Woodlands have duff, prairies have old broken stalks, and savannas have a mixture of the two—except when fire has gone through, but then there’s a layer of ash, which will quickly be shaded by fresh growth in spring or covered with snow in fall.
So in general, mulch is a good thing. But like everything else in the garden, how, where and what you use for mulch depends on circumstances. I have read many gardening manuals that suggest a blanket of two to five or even eight inches of a material such as wood chips should be applied to general garden benefit. This practice is pursued indiscriminately by homeowners and “landscapers” alike.
Phto from Cornell University Gardening Resources,
Plastic or synthetic weed cloth should not be used as an underlayer if at all possible: such materials directly counteract the beneficial purposes of organic mulches. Dyed wood chips have no business in a natural landscape. In addition, lava rock and river stone, while they might serve their purpose in certain situations, are a negative influence around bushes in front of houses. They serve no beneficial purpose, and as normally used, are ugly, besides. And don't get me started on recycled rubber tree ring mats. I suppose they were designed to complement the astroturf in the front yard?
Good Mulching Practice
What is good mulching practice? The short answer is that good mulching is often indistinguishable from the sheet composting described here. My general rule of thumb is to mimic, more or less, conditions in the natural plant communities that your planting area most resembles. (Standard, row-cropped vegetable gardens are a slightly different topic, since they don’t resemble natural communities.)
Shady woodland or savanna gardens often don’t need additional mulch, if you have been allowing natural duff to accumulate. I have an area under a Norway maple, reputedly one of the most difficult trees to plant under, where nothing would grow well. I trimmed the tree high. For a number of years I let duff accumulate, and added extra leaves and cut up branches. I then planted some young natives: elm-leafed goldenrod (Solidago ulmifolia), zig-zag goldenrod (Solidago flexicaulis) and bugbane (Cimicifuga racemosa). Some summer phlox (Phlox paniculata) self seeded and formed a colony, as did some Nicotiana that had grown in a pot. A few starts of periwinkle (Vinca minor) threaded their way around everything, bolstered by some virgin’s bower (Clematis virginiana) I’d planted by the fence, but which established itself on the ground as well. I took a chance on some Virginia bluebells (Mertensia virginica), with big rewards. Today that area is lush and green. Maintenance means occasionally sprinkling some compost around and letting leaves lie where they fall. The plants thrive and multiply, and the whole is a natural extension of my more traditional perennial border. In bare-ish shady areas, say on the side of a house, perhaps where plants are just starting out, I’ll add no more than an inch of wood chips, possibly mixed with chopped leaves, on top of an inch of compost: just enough to nourish the soil and cover the ground, but not enough to invite slugs.
In the traditional perennial or mixed border, among shrubs or in vegetable gardens, a thick layer of mulch really does help prevent weeds, but again, it should used thoughtfully. Among the perennials I’ll add more in a newly planted area, to give new plants a chance to establish without interference. In my old bed, however, I use mulch sparingly, just enough to cover the dirt—the plants grow thick enough to discourage weeds on their own and I’m always trying to encourage many species to reseed themselves. Around shrubs, especially if newly planted, mulch can and should be fairly thick, but applications should be reduced as duff builds up. I also think appropriate groundcovers and small plants should be planted around and among many shrubs in most situations. Most vegetable gardeners know the value of a good thick mulch between rows, how it reduces weeds and necessary cultivation.
Photo from Illinois Department of Natural Resources Schoolyard Habitat Program
Trees in a grassy area should be mulched all the way out to the dripline. They gain protection from mowing damage, and from over fertilization where the grass is being artificially maintained. Their roots will be naturally nurtured by the organic mulch, and won’t have to compete with the greedy turf grass. Why try to grow grass in shady areas anyway? That way only lies heartache and chemicals. Plant woodland or savanna plants instead.
All of these mulching practices help nurture the living soil and allow natural, composting processes to occur by which topsoil is replenished. These are healthy mulches. Like everything in the garden, it helps to be mindful in your practice.