In the fall, many gardeners want to clear away dead leaves, trim back perennials, and give their landscape a clean, tidy appearance. However, research shows that many beneficial insects rely on leaf litter and standing stems to survive the winter.
The popular phrase "leave the leaves" reflects a growing understanding that many pollinators, natural enemies, and other beneficial insects rely on our gardens for winter habitat. Removing all plant debris during autumn may unintentionally remove beneficial insects that contribute to a healthy and productive garden the following year.
Where Insects Spend the Winter
Unlike migratory birds, most insects stay in Illinois year-round. During freezing temperatures, many insects enter a dormant state and seek protected places to spend the winter. Leaf litter, stems, brush piles, and loose soil provide insulation from cold weather and help moderate temperature changes. Leaf litter helps create a microclimate under trees and shrubs where insects can shelter from extreme temperatures and drying winds.
Insects hiding in your leaves
Many gardeners are surprised to know how many beneficial insects spend their winter hiding in leaf litter.
Fireflies
Fireflies spend most of their lives as predatory larvae hiding in leaf litter and soil. They feed on slugs, snails, and other small creatures. Removing leaves can reduce the habitat they need to survive.
Bumble Bees
Only queen bumble bees survive at the end of the growing season. Bumble bee queens hibernate in shallow underground chambers. Leaves and vegetation provide insulation to protect them throughout the winter. This habitat is also used by the federally endangered rusty patched bumble bee.
Flowers are recognized as pollinator habitat. Winter shelter is also important. Even pollinator-friendly landscapes cannot fully support bee populations if they have nowhere to survive the winter months.
Moths and Butterflies
Many moths and butterflies will spend their winter as eggs, caterpillars, chrysalides or cocoons hidden in leaf litter. Luna and polyphemus moths will form their cocoons in the leaf litter. Great spangled fritillary caterpillars will spend their winter close to violet plants. Woolly bear caterpillars will also spend their winter underneath leaves and logs.
Beneficial Predators
Ground beetles, lacewings, and other natural enemies of garden pests often overwinter in leaf litter and plant debris. These beneficial insects emerge early in spring and help suppress aphids, thrips, mites, and other pests before populations build.
Standing Stems Matter Too
Approximately 30% of Illinois native bee species are cavity nesters. This means they nest in hollow and pithy stems. Many other insects also attach their cocoons or chrysalides to standing vegetation. By cutting everything to the ground in autumn, gardeners may remove overwintering sites before insects have a chance to emerge the following spring.
Coneflowers, bee balm, Joe-Pye weed, ironweed and cup plant can provide valuable habitat for cavity-nesting bees and other beneficial insects.
Removing Leaves Reduces Beneficial Insects in Your Garden and Landscape
Research shows that removing leaves can reduce beneficial insect numbers. Gardens where leaves were removed had significantly fewer insects, including large reductions in moths, butterflies, beetles, spiders, and parasitoid wasps.
While one garden may not seem like much, together home landscapes create valuable habitat for insects. Small changes made by homeowners can have a positive impact on pollinators and beneficial insects.
Helping Insects Through the Winter
You don’t need to stop maintaining your garden completely to help insects. Try doing the following:
- Rake leaves off the lawn to prevent them from suffocating turfgrass.
- Place the leaves in your garden beds and under trees as a natural mulch.
- Leave healthy perennial stems and seed heads standing through winter.
- Postpone major garden cleanup until spring.
- Leave some bare well-drained soil for ground nesting bees.
- Leave small brush piles or logs in out of the way spaces in the landscape.
If plants are affected by disease such as blights or other serious issues they should be removed and disposed of properly.
Finding a Balance
You don’t need to have an untidy garden to create a wildlife friendly landscape. Defined bed edges, intentional plantings, and thoughtful design are signals that leaves and stems are being retained for ecological reasons rather than ignored.
This fall, consider leaving a little more of nature in the garden. By leaving some leaves, stems, and other natural materials in place, you can help support fireflies, native bees, butterflies, beneficial insects, and many other organisms that contribute to healthy landscapes. Sometimes the best thing we can do for pollinators and beneficial insects is a little less cleanup and a little more patience.