Waiting on Spring Garden Cleanup to Support Beneficial Insects

With warmer temperatures and spring blossoms we are likely ready to get back into our gardens. Before we get our hands dirty, let’s learn how to support the beneficial insects in our landscapes that are and will be emerging from their overwintering sites. In today’s post we will review some information and tips on how we can support, and not disrupt, the life cycles of beneficial insects like our native bees, when we do any spring garden cleanup or prep.

Plant stems, leaves, and other debris can be home to many beneficial insects during the winter months that are waiting on warmer days before they emerge this spring. Wait as long as you can before removing any plant materials. Photo: M.E. Potter, University of Maryland Extension

Overwintering beneficial insects

Some insects migrate (e.g. Monarch butterfly) to avoid the cold temperatures, but there are many insect species that overwinter (spend the winter months in one of their life stages- egg, larva, nymph, pupae, or adult) in Maryland. Insects like luna moths (Actias luna) who overwinter in the pupal stage in cocoons within leaf litter (see photo below), the great spangled fritillary (Speyeria cybele) who overwinters as caterpillar larvae in leaf litter, bumble bee (Bombus spp.) queens who can overwinter as adults underground, small carpenters bees like Ceratina strenua who overwinter as adults in plant stems, and praying mantids like the Carolina mantis (Stagmomantis carolina) who overwinter in the egg stage as ootheca (an egg case) laid on woody plant stems and other structures. All these examples are of beneficial insects, who provide services like pollination and pest control during their active life stages. This goes to show, even in the cold and quiet winter months, your garden can be full of life!

a luna moth cocoon found in fallen leaves — *Luna moths overwinter as pupae in cocoons made of fallen leaves and silk. In late spring the insect will emerge as an adult moth. Photo: M.J. Raupp, UMD*

When is too early for spring cleaning?

Generally, the longer you can wait the better! Insects do not all emerge at the same time. There are some native bee species that emerge from their overwintering sites as early as March (e.g. some Colletes spp.) and some that typically do not emerge until late May (e.g. Blue-green sweat bees). Due to the changing climate and the diversity of insect life cycles, we unfortunately cannot point to a specific date on the calendar to know all the overwintering insects have emerged from our green spaces. We can look for different cues in our environment to hint at insect emergence.

Before last frost and consecutive warm days

Once we are out of risk of evening frosts and daytime temperatures are consistently above 50°F for several days in a row, many insects will begin to emerge. Otherwise leaf litter and other plant debris are vital for overwintering insects to survive the cooler temperatures. With climate change, and the chances for more drastic temperature changes, fallen plant material becomes even more important for protecting overwintering insect populations. Think of a fallen leaf as a blanket for our beneficial insects!

Looking for spring blooming trees like cherry, peach, or eastern redbuds can clue us in on this year’s seasonal changes and timing when it comes to insect emergence. Once fruit trees have finished blooming, many of our overwintering bees and beneficial insects have likely emerged. Photo: Nancy Lee Adamson, Wild Bee Plantings

Before fruit trees bloom

Many of our fruit trees (along with natives like Eastern redbud and red maple) bloom in early spring, providing nectar and pollen for our early riser pollinators; check out the figure below on native bee and orchard bloom phenology. If you wait for any garden cleanup until these trees have finished blooming (around mid-May), many of our insects will have likely emerged by then. Since phenology (seasonal changes in a plant’s life cycle, such as the timing of bloom) can shift with changing climate conditions, always keep an eye on the trees and blooms around you. A great excuse to get outside and get to know your local plant life.

Before consistent lawn/turf growth

Noticing consistent lawn/turf growth in your area? Cool-season grasses begin their spring growth once soil temperatures are between 50° and 65°F. A general guideline is once lawns need to be mowed it is a good sign it has been warm enough for many of our overwintering insects to emerge. If you have lots of lawn in your space, consider reducing and replacing the lawn with beneficial insect friendly native plants! If you are wondering what you could plant instead, check out Lawn Alternatives. And if you have heard of No-Mow May, check out the Pros and Cons of the No-Mow May Movement and the Controversy Surrounding No Mow May, by Dr. Gail Langellotto.

Sometimes less is more

Less garden cleanup can have a positive impact on beneficial insect populations! Rethink removing plant debris in certain areas of your landscape. Unless the plant debris comes from a diseased or pest infested plant, leaves, stems, sticks and more can be left, relocated, or reused as wildlife habitat. Your plant debris is some animal’s home! Preliminary data from a study conducted by Max Ferlauto, PhD student in the Burghardt lab, at the University of Maryland, Department of Entomology, shows the number of emerging moths and butterflies are reduced by approximately 67 percent in areas where leaves are removed. If you are removing any plant material, consider relocating the materials to an unmanaged, “habitat area”, or to a compost pile after late spring.

Help fight climate change’s impact on beneficial insects by providing shelter to help insects withstand adverse conditions. Consider leaving and/or adding one or more of the following sources of habitat in your green space this spring!

Leaves
Flower stalks/plant stems
Fallen/removed twigs
Wooden logs
Rocks/rock piles

From “messy” to sustainable

If you are worried about your space looking messy from less spring cleaning, there are ways to get creative to transform your and the public’s view of your conservation areas. An opportunity to personalize your green space with unique and practical “signs of care” (also known as “cues to care”).

Signage

A sign in your green space can not only enhance the look but also help educate others. Why are you leaving the leaves? Let others know by adding a sign about how leaves support native wildlife. Look to local artists and organizations to find a sign that works for your space and could convey a science-based message. You can earn a sign from our Bay-Wise Master Gardener program once your landscape is Bay-Wise certified. To learn more, check out our Bay-Wise program page.

Fencing or edging

Even a short fence or edging can make a space look purposeful and cared for. Edging can be made out of repurposed materials (pebbles, stones, sticks, even glass bottles) or can be purchased from most gardening centers or hardware stores. Think of it as putting a frame around the artwork and beauty that is your garden. For ideas check out, Edging Makes Landscape Beds Pretty, Easy to Keep or Landscape Edging Materials.

Tidy, accessible paths

Ensure any pathways, especially areas around public sidewalks, are clear so all can access and enjoy the space and surrounding area. Cut back overgrown plants that may be blocking or obstructing pathways. If you are working in a community garden, consider the accessibility of your landscape so we may create more inclusive green spaces for all. To learn more about accessible green spaces, check out these pages, Create an Accessible Garden for Those of all Physical Abilities and Gardens Are For Everyone: Ideas for Accessible Gardening.

Additional resources

By Madeline E. Potter, M.S.,Faculty Specialist for Entomology and Integrated Pest Management, University of Maryland Extension

Maryland Grows

UMD Extension Home and Garden Information Center Blog