This year, I am trying something new. I am following the advice of Xerces, (the national pollinator protection non-profit) and well-known author Doug Tallamy, Professor of Agriculture and Natural Resources in the Department of Entomology and Wildlife Ecology at the University of Delaware, and not doing the scrupulous fall garden cleanup I have been practicing (and preaching) for over 20 years in my professional career.
In my front yard garden beds, I am leaving the leaves where they fell. In fact, I am exporting some backyard leaves into the front yard so I have an even layer that is three to four inches deep. My small property is all garden, both front and back yards, and luckily, I have leaves in abundance. I have used them over the years as mulch underneath the arborvitaes at the perimeter of my yard where they can remain undisturbed all year. This year, not only am I retaining leaves on my front yard garden beds, but I am going to keep them there year-round as mulch like under the arborvitaes. The best leaves for mulching purposes are ones that curl up to form a fluffy blanket like oak, sugar maple, silver maple, and birch leaves. Do I like how it looks as opposed to bark mulch? Well no, actually I don’t, but I am trying to change my sense of aesthetics. Ask me again in a couple of years.
Why am I doing this? I am doing this because we are losing insects globally at a rapid rate due to habitat loss, habitat fragmentation and climate change primarily (other drivers of insect loss include use of pesticides, light pollution and disease). Insects worldwide have declined by over 45% in the past 50 years according to a number of studies (some say the loss is closer to 75%). We have a serious biodiversity crisis, and some scientists consider us to now be in the 6th great extinction event. Since many insects in our area overwinter in leaf litter, we need to preserve that leaf litter for them to complete their life cycles. Providing insects with nectar or larval (caterpillar) food plants is not enough to sustain them if we don’t also give them places to overwinter! Also, you need to not clean up the leaf litter too early in spring if you are going to remove it. In the Madison area, waiting at least the third week of May if not later is recommended.
As humans, we don’t tend to think of insects often in our daily lives, and if we do, we often view them as nuisances: the spider in the bathroom, the mosquitoes in the back yard, the boxelder bug in the living room window, the paper wasp nest stuck to the underside of the picnic table, etc. But insects comprise the bulk of biodiversity on Earth. They are the base of the food web for many species including birds, reptiles, fresh water fish, bats and amphibians, to name a few. Many animals, especially insectivore birds, depend on caterpillars in particular for fats and proteins to feed their young; they cannot rear young without them. Insects also pollinate a number of our food crops and support the ecological processes we all depend on, whether we realize it or not.
We are oblivious to those ecological processes in our daily lives, but they are, in fact, critical for our survival. Our eight billion lives actually depend on insects and their role in maintaining ecological processes. Insects provide biocontrol of pest insects, such as those that feed on food crops. They pollinate food crops and other plants: about 87% of seed-bearing plants across the planet require pollination by some sort of insect or animal. Plants provide food, cooling and oxygen for all of us. So without insects, most plant species (including many human food crops) would disappear. Insects also recycle dead biomatter, of both plant- and animal-based origins, a huge ecosystem service. They help to distribute plant seeds, play a role in soil health, and more!
The famed naturalist/entomologist/author E.O. Wilson once said “If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos”. Biologist Paul Ehrlich compared the loss of species from an ecological community to randomly removing rivets from an airplane wing. Removing one or two, likely will cause no major damage. But removing 10, or 20 or more, at some point, will cause a catastrophic structural failure and the plane will crash. Insects in this analogy are like the rivets that keep ecosystems and ecological processes going.
As an example of the cascading loss effect, the current ‘insect apocalypse’ as it has been called, is directly related to the disastrous drop in the numbers of North American insectivore birds (as opposed to seed-eating birds) over the past fifty years. This is a loss of three billion breeding birds, a third of our North American bird population. A study Professor Tallamy cites on Carolina wrens, which require 6000 to 9000 caterpillars to raise one nest of young, charts how their populations have drastically declined along with their insect food sources. In England, populations of the spotted flycatcher, a formerly common insectivore, fell by 93% between 1967 and 2016. Worldwide, insectivore birds’ populations have likewise crashed at levels approximating the percentage loss of insect species that support them.
Regarding habitat loss and habitat fragmentation, small populations of insects (and other species) existing in small habitat areas are very vulnerable to local extinction as opposed to larger populations on larger habitat sites. Now we do set land aside for ‘nature’. But only 3.6% of U.S. lands are in National Parks (there is another small percentage of land in state and county parks) and only 12% of the National Park land is federally protected. This is simply not enough land to support biodiversity of all types and the ecological processes that support in turn, us as a species.
What about the rest of the land in the United States that is not in park land? In the U.S., one hundred million people privately own 78.5% of the land. We have 44 million acres of lawn in the U.S., mostly in urban, suburban, and rural private residences. Lawns constitute an ecological desert since they are a monoculture of turf grass (which is often sprayed with insecticides, fungicides and herbicides, to add insult to injury). In total, we apply about four billion tons of pesticides annually across the planet, mostly on agricultural land.
Professor Tallamy posits that in order to preserve natural systems, “We need to give up the notion that humans and nature cannot coexist”; and private yards comprise the biggest percentage of arable land still available. We need to use conservation techniques formerly only used in parks and ‘wilderness’ areas where people don’t live into the spaces people do live in. Tallamy states “Your property is part of your local ecosystem, so whatever you do on your property impacts the entire ecosystem”. Non-indigenous cultures like ours tend to think of land as something we own and that we can treat it however we please. We must rethink this. The land has supported us; now we need to support it. Our actions affect the local watershed, insect and other wildlife populations and the larger environment. Nature is not optional; we all have a responsibility to sustain it.
Tallamy proposes a garden-based solution to the biodiversity crisis, called the Homegrown National Parks® initiative to encourage homeowners to become gardeners, and native plant gardeners in particular. You can check out (and join!) the effort at Home – Homegrown National Park – Regenerate Biodiversity . The idea is to empower people to make a measurable difference by planting native and removing invasives in order to regenerate biodiversity. The ‘hook’ to get people to take action is to allow participants to enter their address on the Homegrown National Parks biodiversity map by planting natives. You don’t have to plant your whole yard in natives, or have a garden that only consists of natives. But you can share on the map all the areas you have planted with natives, whether they are in a single pot or stretched across multiple acres.
While I don’t have only native plants in my little yard/garden, quite a number of the plants are. What if, as Tallamy hopes, everyone on my street used half of their lawn space for native plants? Or a mix of non-natives and natives? What if that happened across the U.S.? That would be 20-22 million acres! We need to have more gardens where nature can thrive in areas that humans live in. And plant choices matter! Ninety percent of insects that support local food webs are specialist feeders; they can only develop on plants they evolved with/on (such as monarch butterflies and milkweed).
Our new garden ethic should be to have many native plants (you can still keep some non-natives, but a good proportion of natives is needed) to support life, sequester carbon, feed pollinators and manage water flow. We especially need to plant what Tallamy calls ‘keystone’ native species that support large numbers of insects, especially moths, that have a caterpillar life stage. Tallamy points out that just 14% of our native plants make 90% of the caterpillar food, so good plant choices are vital. To find more details on these plants for our ecoregion, visit https://nwf.org/keystoneplants . Some keystone plants are oaks, leadplant, Helianthus spp. (such as hairy sunflower or stiff sunflower), and various goldenrod species like showy goldenrod or early goldenrod (don’t plant Canada goldenrod, it is a garden thug). Note that goldenrod is a spreader and needs continual management.
So back to ‘leaving the leaves’ in my yard again. I encourage others to do the same on garden beds, with a few exceptions. One exception is in garden beds that have invasive jumping worms. They feed on organic matter, and fallen leaves are among their favorite food sources. To avoid increasing their population (and the damage they do to our soils), I don’t advocate keeping fallen leaves on those beds. Another exception is if you have a lot of plants that are very susceptible to slug damage, like hostas, as creating a perfect slug habitat surrounding them is not optimal. A third exception is for alpine plants in rock gardens.
I am also not advocating leaving deep drifts of leaves on your lawn (or even garden beds necessarily), especially if the leaf source is a tree like Norway maple which produces large, flat leaves that create a thick stifling mat over plant crowns. The UW Turfgrass Disease Lab conducted a study on the prevalence of snow mold on lawns under leaf litter: basically, there is more snow mold the deeper the leaf litter is in lawns. You can certainly mow over those leaves and let them sift into your lawn as fertilizer, (though this will of course kill any insects overwintering in the leaves) as it at least allows the nutrients to be recycled. But a better choice is to rake those leaves into your garden beds.
Now just because I am ‘leaving the leaves’ does not mean I am not removing diseased perennial stems (like phlox, bee balm, veronicas or monarda with powdery mildew). I do definitely remove those as well as cutting down grasses and stems that are thin and don’t have large piths or species that are not native. I also rake up diseased leaves from lilacs and from crabapples that had either apple scab, red rust or cedar apple rust so they are not a disease reservoir producing inoculum for next season. I did clean up thoroughly around my common lilac that lost all its leaves to Septoria leaf spot this summer, for instance. Unless you diligently hot compost, diseased leaves are best relegated to the yard waste facilties.
I do leave up some portion of the larger diameter perennial stems that are hollow or have a large spongy pith that insects can burrow into for a snug winter hibernating spot. They should be at least 8-18” tall. Those stems should ideally remain up into May or be left to decompose in place over time. I leave up some seed heads on my coneflowers for birds to feed on over winter, as well. Goldenrod plants should just have the seedheads removed if you see insect galls in the stem and left standing (not cut back).
If you’d like to learn more about leaving the leaves, insect decline and what you can do to support insects, and the Homegrown National Park initiative, visit these websites.
Xerces: Leave the Leaves: https://xerces.org/leave-the-leaves
Doug Tallamy videos: Douglas Tallamy | Nature’s Best Hope | Talks at Google
Nature’s Best Hope – Conservation That Starts in Your Yard with Doug Tallamy
Homegrown National Parks: Home – Homegrown National Park – Regenerate Biodiversity
The Insect Apocalypse:
https://www.nytimes.com/2018/11/27/magazine/insect-apocalypse.html
Dave Goulson: Averting the Insect Apocalypse https://www.youtube.com/watch?v=myEGBzt6WTM
