Fallen leaves act as a vital insulating layer for overwintering insects – moths, butterflies, beetles, ground-nesting bees, and other invertebrates use the fallen leaves to overwinter in. Research shows that removing leaves from yards can reduce moth and butterfly diversity by up to 40 percent (PubMed, 2024). When we remove that layer of leaves, we’re not tidying up, we’re displacing hundreds of species that keep the local ecosystem in balance.
I often have to remind myself that not all gardeners are ecologically minded. I don’t want to sit on a high horse or pretend that traditional gardeners lack knowledge or skill. Many are deeply experienced and far surpass my own talents. But the truth is that even skilled gardeners can be poor stewards of the environment.
In the pursuit of “beauty,” we often create inhospitable landscapes for insects and pollinators. Pesticide use, the preference for non-native ornamentals over native species, and the popularity of sterile or pollenless cultivars all reduce biodiversity. Even many well-intentioned gardeners (those who compost, source undyed mulch, avoid chemicals, and plant natives, etc.) undo so much of their good work at the end of the season by sentencing their leaves and stalks to the curb for pickup.
When we rake and bag up leaves and stems, we are taking away from the base of the food chain. Overwintering caterpillars, pupae, and beetles that would emerge in spring are critical food for songbirds, small mammals, and other wildlife.
A study from Penn State’s Department of Entomology shows that areas where leaves are cleared have drastically fewer emerging arthropods come spring – creating a ripple effect up the food web as birds and other predators lose access to the insects that sustain them. The biodiversity we worked so hard to attract and protect is literally being thrown away.
Three things everyone should do during the fall season:
- Leave the Leaves
Fallen leaves support habitat, retain moisture, suppress weeds, provide insulation, and build soil quality as they break down. Don’t like where they fell? Move them! Pile them up in a corner as a brushpile or spread them like mulch over garden beds and around trees – anything but throwing them away. Many butterflies and moths overwinter in fallen leaves – species like the red-spotted purple (Limenitis arthemis) and the banded hairstreak (Satyrium calanus) rely on fallen oak and hickory leaves for survival. So let them break down naturally.
- Leave Perennial Stems and Stalks
Plants support wildlife at every stage of their life cycle, so don’t be in a hurry to cut everything back. Even after summer’s blooms fade and green stems turn brown and hollow, they still serve a purpose.Many small native bees, including the small carpenter bees (Ceratina spp.), nest inside the pithy or hollow stems of plants like raspberry, joe-pye weed, or coneflowers. Leaving 8-12 inches of stems in place provides perfect overwintering habitat for these bees (Oregon State Extension, 2023). Last winter, I observed that the broken stalks of my raspberry canes were home to a few Ceratina bees.
- Be Patient
There’s no hurry to clean up at the first sign of spring. Wait until temperatures stay above 50°F, when most overwintering insects have safely emerged – before cutting stalks back. Allowing leaves to remain where they fall feeds the soil microbes and fungi that form the foundation for the next season’s growth.
Leaving the leaves is part of a larger phenological cycle. What starts with the smallest decomposers ultimately supports the birds and mammals that depend on them. The satisfaction I get from gardening comes from fostering biodiversity and working with, rather than against, the local ecology.