Mulch reconsidered

 “Don’t mulch.” That was the surprising advice from native insect expert Heather Holm. What? That was a recommendation I’d never heard before. Heather’s webinar, “Attracting Bees and Beneficial Insects with Native Plants,” described the life cycles and needs of important native pollinators. Many build nests in the ground, she explained, and they need access to bare soil.

Tawny mining bee nest-photo Andrena Fulva 2d

 
    For years I’ve mulched my garden liberally. It started with an unsuccessful plan to use whole leaves to improve soil in the front yard. When they wouldn’t stay put, I invested in a leaf shredder that chopped the leaves into small pieces that didn’t blow around. Soon I was shredding all our fall leaves to spread on planting beds.

Shredded leaves make useful mulch

 
    I never had enough shredded leaves for everything I wanted to mulch, though, so I also brought in bark mulch from the garden center. In the last five years I’ve stopped using bark mulch and switched to arborist wood chips. 

     This idea came from Linda Chalker Scott, an author and urban horticulturist at the University of Washington who subjects conventional garden practices to objective scientific review. She compared different kinds of mulch head to head and found that the wood chips make superior mulch. They’re tops for holding water in the soil, modulating soil temperature, and suppressing weeds. They promote a health diverse population of soil organisms because they’re made up of a mix of different kinds of tree tissue.

 

Wood chip mulch is nice on paths and around trees and shrubs

    Wood chips fit in with my goal of reducing my garden’s carbon footprint by using locally sourced material. I get them from an arborist who works in the neighborhood.

    Now I’m re-examining my mulch approach because I want to help out native insects. What Heather advised against was bark mulch. She recommended shredded leaves, so I’m OK there. Apparently the insects don’t have a problem pushing their way through leaves to reach the soil, whereas a waxy crust of bark mulch foils them.

    Even better, Heather said, is a landscape where low-growing plants knit together on the garden floor. These plants perform the functions of mulch, and they can also provide food and shelter for native pollinators and beneficial insects (the carnivores that keep leaf-eaters in check).

 

Sweet woodruff has spread more than I'd like, but it does cover the garden floor

    Much of my garden is already provided with a groundcover layer. Two of the major players are sweet woodruff (Galium odoratum) and Canadian wild ginger (Asarum canadense). Between them they cover a lot of shady areas. There’s still not much growing under the shade of evergreens around the perimeter of the yard. This year I’m trying out native wild strawberry (Fragaria virginiana), which spreads by runners. I’m hoping it can survive and spread where other groundcovers haven’t. 

 

Wild strawberry, a native groundcover option

    Meanwhile, there are a lot more wood chips in the yard than ever before. They’ve taken the place of the lawn. Since we joined three adjoining yards to let our dogs play together, happy dogs racing around have worn away almost all the lawn grass. Instead of mud, we’re going with wood chips. I’m hoping the nesting insects will cope.

 

Lawn replaced with wood chips

Shrinking the lawn

Evelyn Hadden’s book Beautiful No-Mow Yards recently reminded me that I still have a grassy lawn. The book spotlights gardeners around the country who have dispensed with lawn, replacing it with options ranging from groundcover beds to meadow gardens to paths leading between garden “rooms” full of beautiful perennials, shrubs and small trees.

Native perennials replace lawn in Robin Wilkerson's garden in Lincoln, MA

    While I’ve long aimed to eliminate lawn, I realized that I’m not ready to give up grass completely. What I’d like would be to reduce it to an area of transition between beds. I still like the look of the visually quiet mowed surface as a foreground for other more exciting plants.

Lawn makes a nice foreground

    Even a low-input lawn like ours is environmentally undesirable. Our lawn uses fossil fuels for mowing, but it’s getting by without fertilizer, weed-killers, or extra water. It’s still a pretty barren habitat for native insects and birds, compared to other ways garden space can be used.

    My lawn-reduction effort started back in the 1980s when I replaced a part of the front lawn with vinca (Vinca minor, also called periwinkle). That wasn’t so much a principled choice as an acknowledgment that grass wasn’t going to grow under the shade of the Norway maple street trees. The groundcover bed has proved to very low-maintenance, needing only occasional weeding to remove maple seedlings.

Vinca groundcover beds are neat and easy to maintain

    Next I dug out some grass around a fish pond we’d installed in a circle of lawn in the backyard. I planted perennials and dwarf trees instead, including two dwarf blue spruces (Picea pungens) that I particularly like. As they slowly enlarge, I’ll need to decide whether to move them and choose something smaller. Meanwhile, they’re doing their part by filling what would otherwise be lawn and offering shelter for moths and butterflies.

Perennials and blue spruce replace some lawn

    Two years ago I took out a big chunk of lawn when I created two perennial beds off the back deck. That and a bluestone path eliminated about 600 square feet of grass. While we had school-age kids, we wanted an open space outside the back door where they and their friends could run around. Now it’s nicer to turn that space over to flowers and pollinators, especially because it’s one of the sections of the yard that gets the most sun.

 

New beds and path where lawn used to be

    Last March I added to a bed with a sheet-composting project. As you can see, the mound of wood chips and compost is starting to settle. With continuing decomposition, after two years, it should sink to the level of the surrounding lawn. Then it will provide a rich environment for flowering perennials. I’m planning to move some there from places that have gotten too shady. If there’s space left, I can add new ones too.

Sheet composting mound is subsiding

    My next plan is to repurpose some lawn space across from the sheet composting. Outside the vegetable garden fence, I could create a cutting garden. It would be nice to grow dahlias, zinnias, and snapdragons just for enjoying indoors in a vase. Why not?

Wouldn't flowers look better?

Groundcover throwdown

Last fall I wrote about uprooting smooth Solomon’s seal (Polygonatum biflorum) under a crabapple that occupies a very visible spot in our landscape. This native plant has spread widely in my yard. I brought home three as a groundcover for shade, and now 25 years later, their descendants are taking over every shady spot in the yard. They may be beneficiaries of our sprinkler irrigation system, which keeps the soil from drying out in the summer, unintentionally catering to smooth Solomon’s seal’s preference.

Smooth Solomon's seal shows up in every shady spot

    This spring I wasn’t surprised to see new shoots of the plant emerging in the section I’d tried to clear last year. It’s hard to remove every scrap of the white rhizomes. What’s needed, I realized, was something to compete with smooth Solomon’s seal. I should choose a shade-loving plant that would be tough enough to hold its ground, but not so aggressive that it would become a problem. Easier said than done. Smooth Solomon’s seal, along with some other unfortunate choices, has taught me that plants can take years to reach a critical population mass that enables a bid for hegemony.

Will fragrant Solomon's seal also turn into a thug? Time will tell

    To avoid bringing home neonicotinoid-treated plants, I’ve learned to look around the garden for things to transplant before heading out to the garden center. I could certainly move some Canadian wild ginger (Asarum canadense) to the area under the crabapple. Its round matte leaves stay clean and fresh-looking through the season. There’s already a lot of it in the yard, though, and its foliage is quite similar to that of bloodroot (Sanguinaria canadensis), which is already growing along the path that delineates the bed. I was hoping for a new look.

What can succeed in territory temporarily cleared of smooth Solomon's seal?

    European ginger (Asarum europaeum), another in the same genus, might also work. While smooth Solomon’s seal claimed territory in the yard over the years, clumps of European ginger have slowly expanded, and now new volunteers are popping up and forming colonies on their own, a sign that the species is finally feeling at home in the garden. I love its shiny round leaves with their subtle pattern of lighter-colored veins. I can dig some clumps from a bed along the driveway to try their luck under the crabapple.

European ginger making itself at home next to the garage

    At the Massachusetts Horticultural Society’s Garden Fair last weekend, I spotted an interesting option, Carex siderosticha ‘Snow Cap,’ with leaves that are almost all white. 

Easy to see why this broad-leaved sedge was named 'Snow Cap'

The volunteer who sold it to me warned that it needs lots of shade, and that’s exactly what it’ll get under the crabapple. With no competition, this rhizomatous, creeping sedge might make a bid for world domination. Let’s hope the energy it expends holding back smooth Solomon’s seal will keep it in check. With so little green leaf surface, it can’t be a photosynthetic powerhouse.

    I’m planning to start with those two and any wandering bloodroot seedlings that I can find and transplant. It’ll be interesting to see what happens under the crabapple once these plants go in. I suspect a guide and referee may be needed.

European ginger and bloodroot coexisting elbow to elbow