In the Garden: Mulch… or Compost?

A bed of brown stuff. It’s actually better for the trees than lawn, but you could fit a few interesting plants in there too. Photo: Charles Kidder.

An American garden writer was on a speaking tour in Europe. She was showing several slides of garden beds, presumably attractive examples. But one audience member was puzzled.

“What’s all that brown stuff?” she inquired.

She was looking at beds that to her eyes were quite bare, with an assemblage of plants, of course—and lots of mulch. The brown stuff.

Unlike many American gardeners, Europeans are not so much in love with mulch. There are many good reasons to put mulch on your plants, as well as some reasons that are less sound.

Mulch conserves water, reducing evaporation from the soil by 15 to 20 percent. When nature provides rain, the drops don’t hit the soil directly, reducing erosion. Also, reducing the splashing of soil and fungus up onto foliage can cut down on plant disease.

Large changes in soil temperatures, especially from below freezing to above, as frequently occurs in the colder months, can heave newly-planted perennials out of the ground. The insulation provided by a few inches of mulch reduces fluctuations in soil temperature, both over the course of a single day, as well as from summer to winter.  

Organic mulches—leaves, wood chips and bark—improve the structure of your garden’s soil and provide a better home for the critters that live in it. And both of these lead to healthier plants.  Inorganic mulches, such as stones, don’t provide any of those benefits and usually look out of place in anything other than a rock garden. 

So, given that we’re pretty much restricting ourselves to organic mulches, what’s the best one?  You’ll see a lot of debate on this, but as far as your plants are concerned, it pretty much boils down to “carbon is carbon,” meaning that the exact type of organics doesn’t matter a whole lot. For example, I might use shredded hardwood on my beds, but put pine mini-nuggets on paths. One caveat: some sources say that compared to hardwood, pine bark on a slope is more apt to wash away in a heavy rain.

One drawback to wood mulches: chips, bark, roots, and shredded hardwood are conducive to fungal growths. Some of these would be considered merely unsightly, while others are more worrisome.  In particular, “shotgun” or “artillery” fungus shoots its spores up to twenty feet. Once they’ve hardened, these pin-head black dots are extremely difficult to remove, i.e., not something you want adhered to your car or siding. If the spores land just on your lawn or garden beds, not a big deal.

One type of mulch needs to be avoided entirely, however: cypress, available in bags at some big-box stores. There is at least one website devoted to the evils of cypress mulch, although not for any damage it could cause to your plants. The issue: bald cypress is not a particularly common tree, being restricted to southern swamps. It does not regenerate rapidly and is vital to the swamp ecosystem. It’s a waste of these good and magnificent trees—some of the oldest in the eastern United States— to grind them up and throw the chips on your garden.

Strictly an aesthetic choice, dyed mulch usually comes in either red, brown or black. Typically made from recycled pallets, you pay more for the added color. Often seen in commercial applications, some find the colors a jarring contrast to your plants. The worst part: dyed mulches suck nitrogen out of the soil, deadly to young plants and brand-new landscapes.

One other type of mulch to consider, and one that struck me as odd at first: compost. I had assumed it would be fertile ground for weeds, but research has shown otherwise. A study by Ohio State University compared three plots: one with 2” of mulch, the second with 2” of compost, and a control plot with bare soil.  The researchers recorded weeding time—courtesy of graduate students, no doubt—and found that both test plots required 1/20 the time of the control, a huge benefit.  Compost also contributes to soil nutrient content much more than mulch does.

When purchasing mulch, you can choose between either buying in bulk by the yard or in bags that typically contain two, or less commonly, three cubic feet.  For planning purposes, one cubic yard (or about 14 bags) of mulch covers 108 square feet to a depth of three inches. Buying in bulk is certainly cheaper. For example, having ten yards of mulch delivered would cost you around $300. For bulk much, you need to have a location that a dump truck can reach, and where you don’t mind having a big pile sitting for a while.  The equivalent amount of mulch in 130 bags would run well over $400 delivered. Although buying mulch in bags is okay for very small areas, it produces way too much plastic waste for larger jobs.

Mulch should be spread no more than three inches deep, and that’s assuming you’re starting with totally bare soil. If you are just re-applying over old mulch, one or two inches should do. Remember not to cover up the basal foliage of perennials and to keep mulch away from tree trunks by six inches. Mulch volcanoes around trees can provide a hiding place for gnawing critters and diseases. If you’re dumping mulch around many small, newly-planted perennials, put the empty plastic pots over the little plants. This will reduce the chance of running your wheelbarrow—or foot—right over the plants. A tip: if you’re moving loose mulch, the job goes faster with a ten-tine ensilage fork, rather than a pitch fork.

Mulch is indeed good for your garden. Just don’t let the brown stuff become an end, rather than the means.


I would find it hard to say there is really anything “good” about a pandemic, but I hope that in these difficult times of COVID-19, you may find additional time to enjoy your garden. 


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