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