Mulch and ground nesting bees - Ask Extension
I was just informed that spreading mulch ( I was going to spread 2-3” of compost soon) could kill our native ground nesting bees which I obviously d...
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Mulch and ground nesting bees #739549
Asked March 18, 2021, 1:40 AM EDT
I was just informed that spreading mulch ( I was going to spread 2-3” of compost soon) could kill our native ground nesting bees which I obviously don’t want to do. Is this true? What do you recommend for mulching around native perennials to improve soil health and help suppress weeds?
We sheet mulched and area of grass last year, planted a bunch of natives in the fall and they’re all still small. I imagine/hope weed suppression will be less of an issue as plants grow and fill in the space.
Thanks for your advice,
Elizabeth
Washington County Oregon
Expert Response
Thank you for your concern about our native bees.
Because about 70 percent of northwestern native bees nest in the soil, people need to understand that certain gardening practices can inhibit the welfare of these small co-inhabitants of our world. One such activity to avoid is covering every square inch of bare soil with a thick mulch layer.
In order to assist native bees, the current recommendation for mulch is to allow a few patches of bare soil within a planting. For instance, maintain several modest-sized bare areas near or adjacent to shrubs and herbaceous perennials, thereby allowing native bees easy access to the soil. Another strategy is to combine some boulders, and/or sizeable rocks, within the planting.
Native bees vary in their preference for what kind of soil they'll use for nesting. Some northwestern native bees prefer to nest in somewhat sandy soil while others will nest in dry, compacted, clay soil such as a hiking path, a country road, or even a cliff side.
Then, too, clues that you've come upon a site for soil-nesting bees may include any of the following telltale signs: One, or more, holes the diameter of a #2-pencil; small piles of grainy soil resembling ant hills; or small turret-like structures which the bees have constructed to protect individual nest entrances.
Because about 70 percent of northwestern native bees nest in the soil, people need to understand that certain gardening practices can inhibit the welfare of these small co-inhabitants of our world. One such activity to avoid is covering every square inch of bare soil with a thick mulch layer.
In order to assist native bees, the current recommendation for mulch is to allow a few patches of bare soil within a planting. For instance, maintain several modest-sized bare areas near or adjacent to shrubs and herbaceous perennials, thereby allowing native bees easy access to the soil. Another strategy is to combine some boulders, and/or sizeable rocks, within the planting.
Native bees vary in their preference for what kind of soil they'll use for nesting. Some northwestern native bees prefer to nest in somewhat sandy soil while others will nest in dry, compacted, clay soil such as a hiking path, a country road, or even a cliff side.
Then, too, clues that you've come upon a site for soil-nesting bees may include any of the following telltale signs: One, or more, holes the diameter of a #2-pencil; small piles of grainy soil resembling ant hills; or small turret-like structures which the bees have constructed to protect individual nest entrances.
