When autumn leaves fall across Clark County, it can be tempting to clear every garden bed before winter. But that layer of fallen leaves is part of a living ecosystem. Within it—and in the soil beneath it—small animals shelter, feed, and survive the seasons when flowers are gone.
At Vancouver Bee Project, we encourage people to think beyond blooms. Flowers provide forage, but pollinators also need places to nest, develop, and overwinter. Keeping some fallen leaves is a practical way to help provide that habitat. The benefits extend beyond bees to moths, butterflies, beetles, spiders, and the organisms that help leaves decompose. [1]
What the research tells us
Leaving leaves is more than a gardening slogan. In a 2025 study published in Science of the Total Environment, University of Maryland researchers Max Ferlauto and Karin Burghardt experimentally removed or retained autumn leaves in pesticide-free residential yards and measured the arthropods emerging the following spring. [2]
Leaf removal reduced overall emergence by 17%. Moths and butterflies showed a particularly strong response: 45% fewer emerged where leaves had been removed, and their diversity declined by about 40%. Beetle emergence also declined. Responses differed among groups; flies and parasitic wasps did not show the same overall reductions as moths and butterflies. [2]
Species that overwintered in fallen leaves, overwintered as larvae, or fed within leaves as larvae were especially affected. The results help explain why removing leaves can remove much more than plant debris. [2]
These findings come from Maryland, not Washington. They do not mean that every Clark County garden would experience the same percentage changes. They do provide direct experimental evidence that autumn leaf management can affect the insects that survive to emerge in spring.
Bumble bee queens need a place to spend winter
For bumble bees, the important distinction is queens, not colonies.
In the typical annual bumble bee life cycle, the old queen, workers, and males die as the season ends. Newly mated queens (gyne) carry the next generation through winter, sheltering individually until they emerge to establish new colonies. Their overwintering sites are separate from the summer nest. [3]
Leaf litter can provide shelter for overwintering queens, including protection over shallow chambers in the soil beneath it. Describing every queen as sleeping among loose leaves is too narrow: the location and surrounding materials vary, and scientists still have important questions about overwintering habitat preferences. [3, 4]
A 2025 paper in The Great Lakes Entomologist documents a useful example. Researchers found a rusty patched bumble bee queen in an urban woodland in Wisconsin, within the upper five centimeters of loose soil beneath leaf litter. This was a single observation of an eastern species—not a study of Washington bumble bees—but it illustrates why protecting both the leaf layer and the ground beneath it matters. [4]
For gardeners, the practical response is to preserve undisturbed patches and avoid unnecessary digging in potential overwintering habitat. A garden can support bumble bees through winter even when no bees are visible. [3]
Moths and butterflies have many ways to survive winter
There is no single winter strategy shared by all butterflies and moths. Depending on the species, they may overwinter as eggs, caterpillars, pupae, or adults. Some use leaf litter; others rely on stems, twigs, bark, or soil. [5]
A caterpillar tucked into fallen vegetation can be difficult to see. A pupa may resemble a dried leaf or remain concealed inside a cocoon. Other species stay above ground: some swallowtails overwinter as chrysalises attached to vegetation, while mourning cloak butterflies overwinter as adults in sheltered places. [1, 5]
That variety matters. Protecting butterflies does not mean that every butterfly needs a leaf pile, or that every brown object in the garden is a chrysalis. It means retaining the different structures that allow different species to complete their lives.
Leaves are one part of that system. Standing stems, woody debris, host plants, and undisturbed soil also deserve space. Clearing all of these features at once can eliminate several kinds of shelter in a single afternoon. [5]
The benefits continue below ground
Fallen leaves also supply organic material to the soil. As they break down, they contribute to the processes that recycle nutrients and support future plant growth.
A separate 2024 study by Ferlauto, Lauren Schmitt, and Burghardt, published in Plants, People, Planet, examined leaf management in suburban Maryland yards. Areas with a history of leaf removal had decomposition rates 17% lower and soil organic carbon concentrations up to 24% lower than areas where leaves had been retained. [6]
Changing leaf management for just one or two years did not significantly reverse those differences. That finding makes a case for lasting habitat patches rather than treating leaf retention as a one-season experiment. It also cautions against promises that leaving this autumn’s leaves will immediately restore a garden’s soil. [6]
How to leave leaves in a working garden
You can keep a usable, cared-for yard while retaining habitat. Start with places where leaves can remain through winter and gradually decompose: beneath trees, among shrubs, or in designated planting beds. If leaves must be moved from a walkway or an area of lawn you use, gently rake them into a nearby suitable area. [1]
Keep habitat leaves whole. Mowing or shredding can destroy insects concealed in them and changes the shelter they provide. Composting recycles organic material, but an actively managed compost pile is not equivalent to undisturbed overwintering habitat. Where space allows, reserve a portion of the leaves specifically for wildlife. [1]
For Southwest Washington gardeners, a useful design approach is a mosaic: leaf-covered areas under woody plants alongside open patches suited to other plants and ground-nesting insects. The goal is to retain appropriate habitat, not to bury every square foot under the same material.
Keep that habitat when spring arrives
Leaving leaves in November and removing them all at the first warm spell can interrupt the protection you intended to provide.
Xerces cautions that there is no single universal date for spring cleanup. Species emerge at different times, and timing varies with climate and location. A warm afternoon—or a simple temperature rule—cannot guarantee that everything has emerged. [7]
Where possible, let leaves remain and decompose in place. If maintenance is necessary, keep it limited and retain undisturbed refuges rather than clearing the entire garden at once. Preserving permanent habitat areas reduces the need to guess when every hidden animal has finished using them. [1, 7]
This fall, choose a patch of your yard where leaves can stay. Give it an intentional border or a small sign if that helps explain its purpose. Then watch how that space changes through the seasons.
Supporting biodiversity includes caring for the parts of the garden we cannot easily see. A queen beneath the leaves, a caterpillar sheltered among them, and a beetle moving through the litter are all part of the community we hope to welcome back next year.
Sources and further reading
Xerces Society. Leave the Leaves! Practical guidance on leaf litter and other overwintering habitat. https://xerces.org/blog/leave-the-leaves
Ferlauto, M., and Burghardt, K. T. (2025). Removing autumn leaves in residential yards reduces the spring emergence of overwintering insects. Science of the Total Environment, 970, 178821. https://doi.org/10.1016/j.scitotenv.2025.178821
Xerces Society. Bumble Bees: Nesting and Overwintering. https://xerces.org/bumble-bees/nesting-overwintering
Herrick, B. M., and Carpenter, S. G. (2025). A bumble bee in a haystack: chance observation of an overwintering rusty patched bumble bee, Bombus affinis (Hymenoptera:Apidae) gyne. The Great Lakes Entomologist. https://doi.org/10.22543/0090-0222.2504
Penn State Extension. Fall Garden Care for Pollinators. https://extension.psu.edu/fall-garden-care-for-pollinators
Ferlauto, M., Schmitt, L., and Burghardt, K. (2024). Legacy effects of long-term autumn leaf litter removal slow decomposition rates and reduce soil carbon in suburban yards. Plants, People, Planet. https://doi.org/10.1002/ppp3.10499
Xerces Society. Don’t Spring into Garden Cleanup Too Soon! https://xerces.org/blog/dont-spring-into-garden-cleanup-too-soon