Mulch Addiction

The United States of Mulch.  Why do we use too much mulch?  What is the alternative?

One of the idiosyncrasies of the built American landscape is our fascination with mulch.  It’s in our yards and gardens; it is in the parking lots of our fast food chains and grocery stores; and it is in our airports and along our highways.  We spread it everywhere.  We spread it thickly.

Our use of mulch is so ubiquitous and so frequent, it is easy to forget how unusual this habit is.  Traveling through Europe or Asia, however, the contrast is clear.  In most other countries, it is the plants themselves that occupy the most space; here, however, mulch is often even more visually dominant than the plants themselves.   I remember a friend from Europe asking me once, “Why are Americans so proud of their mulch?”  At the time, it had not really occurred to me that we use mulch more than other parts of the world, but slowly I too began to see that he was right.  What is curious to me is that our mulch addiction is not limited to socioeconomic class or status.  The liberal use of mulch is as prevalent on wealthy estates as it is on strip malls and tract housing.  And it has little to do with training.  Thick blankets of mulch are specified by landscape architects as often as maintenance crews.  

Where do we get this peculiar habit?  Perhaps part of the issue is that mulch is abundant and cheap.  We’ve always had lots of trees.  Mulch is a byproduct of the large timber industry, making it relatively affordable.  Perhaps our use of mulch is a result of the fact that our landscapes regenerate so quickly.  A recent blog by Noel Kingsbury remarked on how quickly the American woodland regenerates compared to English forests. It’s true: if you leave a piece of cleared land alone almost anywhere east of the Mississippi River, it will likely revert to an invasive-choked woodland within a decade.  Below our lawns and suburbs, there is a feral landscape just waiting for its chance.  Perhaps we mulch (and mow) to keep the beast at bay.  

The beast beneath: left alone for even a few years, wild vegetation eventually takes over. Do we mulch to keep this at bay?

Maybe the better question to ask is not why we mulch, but what is the alternative?    A few weekends ago I went camping with some friends in the Shenandoah National Park.  We camped at a relatively high elevation. I pondered the wild plant communities that were obviously thriving in a relatively harsh environment. Shallow and infertile soils, high winds, and harsh exposures--conditions similar to most urban environments--typified the ridgeline, yet despite this, the ground was almost entirely covered with plants.  A rich carpet of ferns, sedges, and forbs covered even the slightest depressions 

Nature abhors bare soil. With the exceptions of deserts or other extreme climates, bare soil is almost always a temporary condition in the wild.  What is it about the structure and composition of wild plant communities that creates this rich ground-covering layer?  What can we learn from native plant communities that can improve the way we design our plantings--strategies to make our landscapes both more beautiful and more enduring?  

Green mulch. Nature abhors bare soil and fills it will a rich layer of different ground-holding plants

I am happy to say that I am working on a book to answer exactly those questions.  I am collaborating with Claudia West, a brilliant landscape architect and plants-woman who works for North Creek Nurseries.  The book is focused on native planting design, paying particular attention to how understanding the layers and dynamics of plant communities in the wild can improve our designed plantings.    The book will be published by Timber Press.  More on Claudia and the book later.

The alternative to mulch is what Claudia calls “green mulch,” that is, plants themselves.  A lot more plants.  In a recent discussion with Claudia, she pointed out that our habit of continually adding mulch year after year artificially keeps our plantings in a perpetual establishment phase.  Vertically layering our plantings with different kinds of forbs, graminoids, ferns, and woody species to form a dense carpet can indeed create plantings that need little or no mulch.  

This process of vertically layering requires a lot of plants.  Woody shrubs must be under-planted with herbaceous species.  Tall grasses may need to be under-planted with lower sedges.  Perennial borders will require multiple layers of ground-holding plants to support taller accent species.  The goal of this kind of layering is not just to reduce our use of mulch, but also to create more stable, enduring, and even more beautiful plantings.  

Verbena bonariensis and Phlomis tuberosa. Two self-seeding plants in my garden that I hope to encourage

This past year, I stopped mulching my perennial border.  It was a fascinating experiment.  Instead of mulch, I gently worked a bit of compost in the spring with a fork--being careful not to cover the ground, but instead get the compost into the soil.  In most places, I found that the plants I had were dense enough already to choke out any weeds.  In a few places, weeds appeared under taller, upright perennials.  Those areas highlighted for me a missing “layer” of plants that I will add next spring.  The other more surprising benefit was how much self-seeding happened as a result of not mulching.  The appearance of these self-seeders added a much needed spontaneous element to the border, threading it together more fully than what I could have done on my own.  This look of spontaneity and naturalness is incredibly hard to create.  Next year, I’m hoping self-seeders play an even larger role in the garden.

I look forward to developing these ideas more fully and sharing our research  along the way.  Stay tuned . . .