Mulch has been a hot topic in the horticultural world as of late. A scathing essay by Radovan Hajek, a co-owner of US Perennials Nursery, on the American aesthetic of too much mulch and too few plants has been making the rounds in popular garden newsletters. Hajek writes, “Mulch became more important than the plants themselves. Plants are the minority, spaced about 2’ apart. They will never touch, intermingle, grow together and will never create harmony, contrast or drama. They’ll just live their separated, sad and struggling lives.”
The anti-mulch movement has been afoot for a while; Hajek quotes in his essay designer, plantsman, and author Roy Diblik, who wrote extensively about the negative impacts of mulching in his 2014 book The Know Maintenance Perennial Garden. Likewise, ecological landscape designer Larry Weaner, discouraged mulching in his 2016 book Garden Revolution. Conservationist and native plant educator Cathy Ludden, who is a board member and gardener at Nature Center at Greenburgh, says hearing Diblik speak inspired her to ditch the annual application of mulch. “Every year, I laid down a beautiful layer of sweet peat mulch because it looked so neat and so attractive, and that’s what everybody said you should do,” she recalls, but Diblik made her wonder why.
“As gardeners, we know, it’s so important to know where a plant evolved to know what conditions it likes,” says Ludden. “I realized that so many of these plants want to propagate themselves. They do that by sending out runners, by dropping seed, or by expanding at the crown. And none of those methods of propagation are possible if they’re sitting in two inches of shredded bark.” As soon as Ludden stopped mulching, her perennials were able to grow and expand, self seeders popped up, and spring ephemerals emerged. She never looked back.
Why is frequent mulching a bad idea?
Above: Instead of buying mulch, consider mulching with leaves this fall. Photograph courtesy of Refugia, from Fall Gardening: 15 Ideas For What to Do With All Those Leaves.
One simple idea underlies the argument against applying mulch to garden beds: It’s unnatural. As Diblik writes in his book, “There is not a plant on earth that has evolved living in a pile of wood chips.” What is natural is more plants. “Filling those spaces with plants is better ecologically, it’s better from a plant health perspective, and it’s significantly less work,” says ecological horticulturist Rebecca McMackin, who writes the newsletter Grow Like Wild!
Thick mulch inhibits perennial growth, prevents plants from self-seeding, and may suppress some tender plants from emerging at all. For example, once Ludden stopped mulching she saw trout lilies volunteer and lobelia cardinalis popping up in many places she never planted it.
Mulching also disrupts the soil’s natural ecosystem. Explains McMackin, “When we rake leaves away and put down mulch, we’re interrupting the processes that actually build soil. Over time soil can get depleted because they’re not being fed with this organic matter and fungal and insect communities that really create the soil.”
Worse still, mulching doesn’t even work that well at what it’s supposed to be doing, including suppressing weeds. As Weaner and Thomas Christopher write in Garden Revolution, “[Mulch] will not long deter neighborhood bullies such as Canada thistle, Japanese knotweed, and Asiatic tearthumb. And once they gain a foothold in the mulch, the bullies will be hard to displace.”
In some instances, mulch can also inadvertently repel water. As horticulturist Linda Chalker-Scott, Ph.D., of Washington State University explains in an essay titled “The Myth of Pretty Mulch,”: “Bark [mulch] does not function like wood chips in its water holding capacity. Bark is the outer covering of the tree and is heavily suberized to prevent water loss. Suberin is a waxy substance that will repel water, and in fact helps explain why fresh bark mulch always seems dry. Wood chips, on the other hand, consist primarily of the inner wood, which is not suberized and has the capacity to absorb and hold moisture.”
Finally, in some extreme instances, deep mulch can restrict airflow into the soil. “I’ve seen mulches go anaerobic, and they can change soil chemistry in a way that you don’t want to,” says McMackin.
So when is it appropriate to mulch?
Above: Ludden says mulching around shrubs is okay if you want a tidy look, since it doesn’t impede their growth. Photograph by Liesa Johannssen for Gardenista, from Architect Visit: Barbara Chambers at Home in Mill Valley.
Use mulch strategically when you first plant perennials. McMackin says, “I will mulch those areas in order to hold the moisture and prevent weeds from seeding or from germinating while those plants are getting established with the understanding that eventually the plants will fill in those spaces.”
Ludden also recommends mulching when planting a shrub border. “I would put shredded bark mulch down because it keeps moisture in the soil and prevents weeds, and it looks neat and tidy,” she says, noting that the shrubs don’t propagate themselves the way perennials do, so you’re not preventing growth. Mulching around trees and shrubs also reduces the likelihood that someone will run a lawnmower over their roots, but even better would be to plant a soft landing.
If mulching woody plants or trees, use arborists wood chips and be sure not to let the mulch cover any of the bark: The root flare at the base of the trees should always remain exposed. If you have existing mulch volcanoes, remove them (arborist Basil Camu of Leaf & Limb explains how in this video).
Vegetable gardeners may also want to mulch, says Ludden, especially if it’s something that you can till into the soil along with whatever is left of the plants at the end of the season.
Finally, McMackin says you can use mulch when you want to shift the soil composition. For example, if the soil is too basic, you might add pine mulch. “The change is not very serious, but it will start those processes,” explains McMackin, who says to think of mulch as an amendment you’re applying to the top, with the understanding that it’s going to be integrated and building soil in the future.
What are alternatives to mulching?
Above: Denser planting means fewer weeds. Photograph by Neil Landino, courtesy of Hollander Design Landscape Architects, from Garden Visit: 10 Lessons from a Coastal Landscape Designed for Deer Resistance.
If you’re worried about weeds, plant more densely. Instead of maintaining a sea of mulch with plants in it, position the plants more closely together and let them naturally grow towards each other. For anyone worried about maintaining air flow, McMackin says, “That just wouldn’t happen in the natural world.” She notes that what is more important is to maintain healthy soil. In Garden Revolution, Weaner and Christopher note that you should also think about varied below-ground growth habits to inhibit weeds. And yes, you may have some weeds. “Weeding and watering are important in the first season or two until the perennials begin to fill in,” notes Ludden. “As plants expand naturally, and even seed themselves into open areas, weeds become less problematic.” (See The Garden Decoder: What Is ‘Cramscaping’? (And Why Is this Trend Here to Stay?)
You can also plant a “green mulch” or groundcover. Ludden has had success using Canadian wild ginger, ferns, and carexes, including Carex Appalachia and Carex pensylvanica as soft underplantings between larger perennials.
Above: European meadow sedge (Carex remota) is a durable green mulch. Photograph courtesy of Greenlee and Associates, from The Garden Decoder: What Is Green Mulch?
You can also mulch with clippings. McMackin suggests mulching with the plant matter from the previous season, noting, “[Plants] really want to be in a mulch made up of their own leaves and stems.” Diblik describes using a similar method in The Know Maintenance Perennial Garden, noting that, “The litter is in much bigger pieces than if it were mowed, so we cut some of the stems into smaller pieces, so that they’ll fit comfortably around the plants.” He adds, “I must admit, the first time I did this it was difficult not to run for the rake.”
If you still feel the need to mulch, all the experts recommend swapping bark mulch for a local leaf mulch or compost. Leaf mulch or compost can provide the “neat” look that you may prefer without inhibiting the growth of perennials.
Another solution is to give your garden beds a mullet. When working in Brooklyn Bridge Park, McMackin and her team used a neat-in-front-wild-in-the-back look, which she calls a “mullet” approach to mulching. “We would rake out leaves in the first foot or two of the garden and then put a clean edge of mulch. Then you can get away with a wilder look in the back, if you do that.” If you can’t see yourself quitting mulch, don’t let it get too deep. McMackin says an inch or an inch and a half is all you should ever need.
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