For a few years, once every fall, I cleared the leaves off the grounds of our local sailing club. Family changes mean I'm not involved there anymore, but I still remember the rhythm of it, wheelbarrow after wheelbarrow of oak and maple, hauled to the compost pile at the back of the lot.
I never once stopped to ask what I was actually moving. Then I came across the work of the Xerces Society, and a University of Maryland study that put numbers to what's lost.
What's actually in a pile of fallen leaves
A leaf layer isn't just dead plant matter waiting to decompose. It's a slow-release pantry, an insulation blanket, and, for a surprising number of species, a nursery.
Luna moths spin silken cocoons that overwinter directly among fallen leaves, often disguised to look like dry foliage. Red-banded hairstreak butterflies lay their eggs on fallen oak leaves. Many native bumble bee queens overwinter in small chambers underground, often in sheltered soil beneath a layer of leaves.
The Xerces Society puts it plainly: "Leaves are not litter. They are food and shelter for butterflies, beetles, bees, moths, and more."
When fall cleanup moves those leaves to the curb, or across a lot in a wheelbarrow, the overwintering lives attached to them often go with them.
The numbers behind the rake
That last sentence isn't a guess. Researchers at the University of Maryland studied what actually happens when leaves are removed. The numbers are harder to ignore than the general advice.
In a study published in Science of the Total Environment (2025), Ferlauto and Burghardt found that in yards where leaves had been cleared, butterfly and moth emergence dropped by 45% the following spring. Beetle emergence fell by 24%. Spider numbers declined by as much as 67%.
A separate study by the same lab, published in Plants, People, Planet (2024), looked at what leaf removal does to the soil itself. In yards where leaves had been hauled away for anywhere between 3 and 30 years, organic carbon in the top 18 centimeters of soil was 24% lower than in yards where leaves stayed. Decomposition rates, a measure of how quickly organic material breaks down, were 17% slower.
That's two processes disrupted by the same action: the life above the soil loses its shelter, and the life within the soil loses its food.
The quiet trade-off
This isn't about letting a yard go wild. It's about understanding what a leaf layer actually does:
It insulates. A natural layer of fallen leaves buffers soil temperature swings and helps retain moisture through winter.
It feeds. As leaves break down, they return organic matter and nutrients to the soil. It's the slow, patient work that a bag of fertilizer can't replace. The 24% carbon gap in the UMD study suggests this process compounds over years.
It shelters and protects your garden. Beyond cocoons and queens, leaf litter hosts assassin bugs, lady beetles, parasitoid wasps, and ground-dwelling spiders: predators that keep pest populations in check when spring arrives. The Xerces Society notes that only about 2% of described insect species are considered pests. The vast majority play important roles in ecosystems, from pollination and pest control to decomposition. Many of these species depend on undisturbed leaf litter or other sheltered habitat to survive the winter. Remove that layer, and you may lose part of your pest control crew before it ever clocks in.
Removing all of it, especially by bagging and hauling it off, doesn't just tidy the ground. It interrupts a cycle a garden depends on, year after year.
Context matters
Honestly, if I had started lecturing fellow club members about overwintering Luna moth cocoons while standing next to a dock in late October, I'd have gotten some very polite, very confused looks. And rightly so. A sailing club lot isn't a pollinator garden. Leaves on walkways are a slip hazard; leaves clogging drains flood the clubhouse; leaves on the slipway make hauling boats dangerous. The cleanup had a reason.
Context matters. "Leave the leaves" is not a universal rule. It's an invitation to ask, each fall, where the leaves need to go and where they can stay. A storm drain is not a garden bed. A boatyard is not a backyard. But the strip of soil behind the fence, the base of the oak by the parking lot, the quiet corner no one uses: those places are habitat, if given the chance.
What to do instead
You don't have to leave every leaf exactly where it fell. The Xerces Society suggests a middle path:
Rake leaves into garden beds instead of bagging them. They mulch, insulate, and feed the soil in place.
Pile them around tree bases to protect roots and build soil organic matter over time.
Keep heavy layers off turf and storm drains, but let the rest stay.
Avoid shredding with a mower. Whole leaves provide better cover for overwintering insects and eggs. Shredding can damage or destroy them.
If cleanup is necessary, wait until nighttime temperatures are consistently above 50°F (10°C). That's a useful rule of thumb from several extension programs: a point at which most overwintering insects have emerged. Earlier in spring, many are still sheltering in leaves, stems, and soil.
Small shifts. Big difference.
Why this matters more than it looks
There's a bigger picture under every leaf pile. Pollinators across North America face many pressures, from habitat loss to pesticide exposure and climate change. The UMD research makes one thing clear: even ordinary cleanup habits contribute to the loss of places where insects shelter and survive.
Leaving leaves is one of the smallest, cheapest, most immediately effective counter-moves available to anyone with a yard, or a wheelbarrow and a Saturday.
No special equipment. No extra cost. Just a different relationship with the season.
Field Notes explores the intersection of soil, science, and growing — through curiosity, careful research, and a willingness to question familiar assumptions.
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Sources
- Ferlauto, M., Schmitt, L. & Burghardt, K. (2024). "Long-term leaf litter removal reduces soil carbon and decomposition in residential yards." Plants, People, Planet 6(4): 875–84. DOI: 10.1002/ppp3.10499
- Ferlauto, M. & Burghardt, K. (2025). "Removing autumn leaves in residential yards reduces the spring emergence of overwintering insects." Science of the Total Environment 970: 178821. DOI: 10.1016/j.scitotenv.2025.178821
- Xerces Society for Invertebrate Conservation – Leave the Leaves campaign
- Xerces Society – Tiny Places for Tiny Animals
- Xerces Society – Put Down Those Pruners
- Alabama Cooperative Extension – Leave the Leaves: Benefiting Insects & Wildlife
- University of Maryland Extension – How to Protect Pollinators in the Slow Season
- Xerces Society – Leave Leaves for Natural Pest Control
- Backyard Ecology – How to Do Spring Garden Cleanup for Pollinators and Wildlife
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