From away to garden.com and Robinhood Radio.com, this is Away to Garden with Margaret Roach. You're a weekly invitation to dig in and grow. Every gardener has certainly heard the rallying cry each recent autumn to leave the leaves, invoking us to go gentler with our cleanup to support a diversity of beneficial earned vertebrates who call the fallen leaves their home. Now a recently published research study calculates just what the impacts of leaf removal are to which organisms and also offers insights into how and where in our landscapes we can leave the leaves to create habitat with the most positive impact. Max Frilotto, the Maryland State Entomologist, is one of the scientists who conducted the new research, and he's my guest today, so more in a moment, but first, these messages. Underwriting support for a Way to Garden provided by Colorblends, wholesale flower bulbs, a third-generation bulb company offering top-sized flower bulbs directly to landscape professionals and ambitious residential gardeners on the web, colorblends.com. And by High Moeng seeds, Wolcott Vermont, professional quality vegetable, flower, and herbal seeds that are 100% organic and non-GMO project verified. On the web, Maryland College Park published research on the impacts of leaf removal, resulting from their two-year study in 20 residential suburban Maryland yards. In March this year, Max Verlato and Karen Berghardt and ecologist and associate professor at the University of Maryland College Park

published research on the impacts of leaf removal resulting from their two-year study in 20 residential suburban Maryland yards. Max is here to talk about their takeaways and how the data they gathered can help inform gardeners seeking to develop their own more ecological, full cleanup plans. It's good to talk to you again, Max. Hi. Hi. Glad to be here. Yes, so we did a recent New York Times garden column together about your latest research with Karen Burkhart. And I think I said to you at the time, to me that research, you know, I'd heard about leaves the leaves, but this was like leave the leaves by the numbers. It's like you really collected data, you know. It was amazing. So tell us, you know, about the basics sort of briefly, tell us how did the study take shape? What did you do? What was the protocol so to speak? Yeah, sure. So we use these things called emergency traps, which are these tents that you basically place over the earth and anything that emerges from that piece of land gets collected. And so in these suburban yards, as you mentioned, we placed those emerges traps over areas where leaves were raked away and leaves were retained. So we were able to really see everything that was emerging from the ground in the winter or after the winter, which is the period of time that we're concerned about during the leaf litter removal period. Right, and so how, like, so they were pairs, so to speak of of these traps and one had leaves, one area had leaves and one didn't in each case and how big were the spots, how big were the traps. So we manipulated the leaf litter in one meter square quadrats and the emergence traps over those quadrats in areas where we removed or retained leaves. So that's not really very big and yet when I read the numbers, I mean, you know, it's a little larger than a square yard, yes, a square meter. Yeah, that's a square meter. Yeah, so it's not miles and miles and miles and miles.

And yet when I read the numbers, you know, come spring or like in March when you put these emergence traps up through I guess what the end of June was it each year? Yeah, March through June. March the end of June. And we collected almost 2000 insects emerging, insects and spiders emerging from that square meter of yard. In each one that had leaves, yes? Yes. I mean, that's a lot. That's a lot of life. That's a lot of life. And you don't think about your yard producing that much abundance and biodiversity, but that's what we found. And which organisms were you counting? You weren't counting like earthworms or anything? No, the earthworms and decomposing species, like springtails, those, you know, we had even more of those. These were just butterflies and moths, beneficial parasitic wasps, spiders, beetles and flies. And basically when you removed leaves, we saw a decrease in a lot of these groups. So when you removed leaves, we found that the average abundance of butterflies and moths was reduced by about 45%. 45%? Yeah, 45%. Oh. Spider emergence declined by 56% and beetle emergence declined by 24%. So we're seeing that yes, these small sections of our yard, which produce so many insects and beneficial species. If you remove the leaves, we're seeing declines there. Right, so now people are probably like, wool, but what is, what is a, you didn't mention parasitic wasps just then you had mentioned them earlier, but what am a gardener? Why am I thinking about spiders? A lot of this is about the checks and balances systems, right? It's like the whole system has to be in place. It's not just we've all heard in the Levy Leads campaign. We've especially heard about the butterflies and moss and their caterpillars, which then of course are the primary food source for baby birds, especially songbirds. And that's so critically important. And that's been highlighted to us as part of this campaign. But it's not quite that simple. It's not just those doctrines. Yeah, but in your yard, you want to have a thriving ecosystem. That means thinking about the prey and the predators. That occurs at the insect level, just like it occurs for mammals and birds. So yes, it's really important to have butterflies and caterpillars to feed birds, but also it's great to have beneficial biocontrol. These are natural enemies that we have in our yards that take care of our best problems. So things like spiders, certain ground beetles, and definitely parasitic wasps, which are tiny wasps, they can't sting humans, but they will lay their eggs in different pest species and reduce their numbers. So if you have outbreaks of aphids or tobacco hornworms on your tomatoes, there are these parasitic wasps that will control those species. So if we do anything to interrupt their success in our habitat, whether by in some of the cases that the numbers you mentioned a couple of minutes ago, by leaving the leaves, we reduced the percentage of emergent individuals of those groups of invertebrates. Right. Invertebrates, you can screen, you know, a pesticide might take, you might get ready to problem in the short term, but in the long term, if you're killing both the prey and the predator, eventually that outbreak could come back even worse because you're not gonna have anything to control it. So anything that is gonna disrupt those food chains in the long run is gonna be damaging. Right, so if we want, if we want, you know, somebody to take care of our aphids and our tobacco hornworms, we'd better make sure that the food that they want is around otherwise they're not going to find our environment very attractive. I'm oversimplifying, but you know what I mean. It's, yeah, yeah, yeah. So, so there was these declines in abundance, I think you told me when we did the time story, you would call it the total number of individuals. And also fewer species you saw in some cases, yes. Yeah, so butterflies and moths had a reduction in species richness or the number of species by about 44%.

Oh my goodness.

Yeah, and what we're seeing was it wasn't just that the species richness was being reduced, but also the composition, the different types of the species that survived had changed. So specifically, species that mine leaves, they're called leaf miners, or species that overwinter as larva, or overwinter within the leaves, that those are their life history traits, we say. Those were the species that were harmed the most by removing leaves. And on the predator side, we found that the parasitoid wasps that feed on the leaf minors and feed on the larvae that are overwintering, declined just like those prey species did as well. So we can see the entire food chain being disrupted by removing leaves. So many years ago as gardeners, and especially I've been an organic gardener for decades and many, many years ago, you know, it was a big aha moment where it was like don't put, don't bag your leaves and put them out at the curb, you know, be more sustainable, keep them there,

utilize those resources, build your soil, use it as mulch,

mow over it on the lawn, shred it and let it decompose into the soil of your lawn, and blah blah blah. In other words,

keep it out of the landfill and that's a great idea. That's a great idea, but it doesn't do what we're

just talking about fostering supporting this food chain,

and creating habitat for all of these species to live their life cycles out. So, what can I mean, I'm going to still say I believe that compared to sending it in a plastic bag to the landfill. We may have to, some leaves may have to get maybe end up in the compost or some leaves may have to end up. Sometimes we just have too many in certain configurations of our home landscapes or whatever to let them all lie on every square inch. But what should we be doing and what can we be doing and which actions don't support these organisms that live in the leaves and so forth? Like, how do I know what to do? What are my best and worst options so to speak? Because it's confusing. I'm a huge proponent. I'm a huge proponent of composting leaves for your garden, but as you mentioned, by doing that, you are going to be killing those over wintering species. So is it the heat of the compost? What do you have? The compost that is running strong and hot, it will kill those species. but also just the depth of that compost pile is going to be disruptive as well. So really what we're saying is you don't have to, you know, leave the leaves over your entire yard. As we, as I mentioned, just a small square meters producing so many insects. So if you have too many, you can compost, you know, what you need to, but by leaving leaves and not composting them, you're allowing for those life cycles of these different insects we're talking about to complete. And some other things you can do is take the leaves from an area that you don't want them and just move them to a new area. A lot of the insects are overwintering within that leaf material. So by moving it you're just basically moving them to a new home over the winter. So moving them whole, not not shredded or you know not that put through a machine of some, but moving them whole. You found that shredding leaves was almost as bad as from as removing them and backing them. So removing them whole, placing them at the edge of your yard, those are all alternative practices. So moving them around. And in terms of kind of identifying where are there sort of like areas of maximum impact, positive impact, I believe when we did the time story, we talked about thinking about, so here I've made a pollinator garden in my backyard, let's say, okay, let me visualize all those creatures that are living in there in the fair weather months. Where are they going to go and complete their life cycle, procreate whatever, what's gonna happen next to them? And maybe have some kind of think about you utilizing that area or an adjacent area or kind of, or if I have trees and letting leaves lie under trees and creating a bed under the trees and things like that. Like what kind of strategies is that kind of thinking? Is that what you're doing? Like when you look around. And you know, we did look at this and we found that leaving leaves and areas where they had previously been removed year after year was more beneficial than just leaving them in an area where you always leave them. So that leaf material is a habitat resource. And so by providing it and otherwise, there in area you're attracting those insects to that to that protective habitat, overwintering habitat. In areas where you have flower gardens, where you have native plant gardens, those are all ideal places to retain your leaves. Yeah, I would think so. To me, that's, again, when we spoke before at the time, that was kind of what I was visualizing when you were sort of walking me through the research and when I read it on my own and so forth after our conversations. I was kind of visualizing the other thing I was visualizing is that, huh, okay, the fringe of my property, for example, I have a lot of mature trees, you know, as many people do, you know, the biggest trees sometimes are along the property boundaries or whatever. And I thought, okay, so those oaks, what if I can make those have their own leaves beneath them? If I can create beds, so to speak, and say, these are my safety zones. These are places where I'm going to leave the leaves because that would seem to be a very natural, ideal kind of situation. Yeah, there's a term that's been discussed called soft landings. Right. The idea where you have those areas under trees and you keep them natural. And if you need to move leaves to those areas, as long as you're not creating huge leaf piles and you're just kind of moving them from one area to another, you can create those protective habitats so that all of those species that live on the trees during the summer and spring can move down to its roots to the leaf layer that's there during the fall and winter. Mm-hmm. And you just said huge leaf piles. And we're not talking about it, is we're not saying take every leaf, whole pile them on tarps and drag every single leaf on your property onto one bed under one tree. So this is seven foot deep. Right, I mean, it's a little bit... That's not good. That's not good. Yeah. The insects, they're cute to seasonal changes. And also energetically, it's very difficult for them to climb, you know, out of it, as you said, a seven foot pile of leaves. So they want their environment to be as similar as it would be on a forest floor. So imagine walking through the woods on a hike, the leaf layer that you're seeing around is the depth that we're talking about. Okay. So not deeper than that. So it's not giant, giant, giant piles of leaves, which also with some other some of the herbaceous plants at that layer yeah oxygen levels are lower it's just not a great habitat to be overwintering insect at the bottom of a massive pile of leaves okay and. And similarly, you're not advocating that again, using this kind of like walk around and look and try to draw inferences by thinking about where are these creatures and where are they going to go next month and three months and six months. You know, in other words, to have a whole year, to have their whole life cycle however long it is and their next generation and next generation survive in this area where I may have attracted them with my planting methods and so forth. I mean, it is a garden after all. So I'm not just going to dump seven feet deep of leaves behind my garage either, right? That's not the the whole answer. Yeah. Yeah. And it's it's thinking about the whole life cycle, as you mentioned. So if you're attracting the insects in the summer with your native plants or your pollinator flowers, you don't want to remove the habitat that they rely on over the winter. You're basically just attracting them to kill them later on. So it's those areas that can be the best places if you must leave your leaves in only one area, not the whole yard. Those are the areas to prioritize. Right. And you just mentioned winter. And so a lot of us, again, and it was leave the leaves, don't clean up so scrupulously in fall, be a little messier, et cetera, because of overwintering habitat. We were, this is what we've learned so far because again, this is a fairly new idea for a lot of us and we're trying to, and we're not scientists, we don't have your expertise and we're trying to take it all in. So we've learned about the overwintering habitat idea and who's in that leaf litter in the off season. But it doesn't end there, does it? The importance of that habitat doesn't end there, does it at the end of winter? Yeah, our experiment was to remove the leaves in the fall and then we placed those emergence traps in the spring to early summer. But we did not notice any declines in the number of bugs emerging. So there was a thought that at some point maybe when the ground hits 50 degrees or all these these other potential times, there was going to be a cliff and most of the insects would have emerged and now we're okay to remove our leaves. We didn't see that. We saw that insects kept on emerging throughout the summer. So that in July we were actually getting more insects emerging than we were in March and April. So yeah, I would say that we're talking about over wintering and that is what we specifically study, but it doesn't look like there's much evidence for there being a time where everything is emerged and it's okay to clean up. A lot of species

actually have two generations. So they'll have a generation in the spring and then they'll also have one in late summer. So this leaf habitat is valuable all year round. Right, right. Well, and if we think about it, we're in a way emulating or thinking, we're evoking this sort of duff layer, the forest floor, you mentioned before, is the closest thing we know in habitats. So nobody cleaned up the leaves there at any time. Do you know what I mean? It was a forever thing. The detritive wars, all the other creatures who you didn't count in this particular study, but who we know something about, they were doing their work down below on the oldest stuff, right? Which was getting incorporated into the soil, the organic matter was getting incorporated into the soil. So it was a constant, again, food chain. Yeah, and I mean, there are examples in history where humans have removed leaf litter from forests. Like in the middle ages, they would use that material for bedding for their livestock.

And there have been studies that have shown that those areas where the leaves have been removed for centuries have lower soil carbon levels. You can, you know, hundreds centuries after that practice that's. So, the removal of this material has long lasting implications. We have maybe two, three minutes left. And let's talk a little bit more about that, because I think a year prior, I think you published work about more research, earlier research about soil carbon and about what you were finding.

I think it was from the same properties I believe, but earlier inferences, yeah, about that. So we looked at soil carbon and decomposition. We found that areas where leaves have been removed year after year as a historical

practice within yards had a reduction of about 24% of soil carbon was reduced. And the soil carbon helps in what's its role it helps with? So carbon and soil organic matter really are valuable as I guess you could say pervayers of different soil qualities. So soil carbon, having higher soil carbon means Your soil is more nutritious. It means it holds water better.

Right.

It means...

Struck. when means your soil is more nutritious, it means it holds water better. It means structurally, it is less compacted. And then, of course, thinking on the big picture, so carbon is important for carbon sequestration from our app. So soil carbon is very important to the systems of earth. So that was another, some of the earlier takeaways. And that's not quick. Like you said, in the places where you added leaves, you saw almost not immediate, but in that same season, you could see creatures were utilizing it, whereas repairing this loss of soil carbon doesn't come back the next year. Right, exactly. And we would say that this would be a legacy effect, of leaf removal. The carbon is being reduced by 24%, it's not coming back the next year. Or probably anytime soon. Yeah, exactly. Yeah, well Max, for a lot of, I mean, the numbers really did it for me. I mean, it made me want to learn more and more about each of the creatures, you know, and how to support

them. And the intricate, you know, relationships between them and so forth. So I just found it fascinating. And of course, I'll give links with the transcript of this show over on A Way to Garden.com, where people can read the research and our Times article together and so forth themselves. But I'm so glad to speak to you again. And thank you for making time I know you've got lots and lots and lots going on so thank you. Absolutely.

Great to talk to you. And I hope I'll talk to all the rest of you again soon too. Now don't miss an episode. You can subscribe free to the podcast version of the show on Spotify or Apple podcasts. And you can find me anytime at away to garden.com and on Facebook and on Instagram as at a way to garden. And happy Gardening and leaving the leaves, meantime. Underwriting support for a way to garden provided by Colorblends wholesale flower bulbs, a third generation bulb company offering top-sized flower bulbs directly to landscape professionals and ambitious residential gardeners on the web, colorblends.com. And by high-mo Seeds, Wolcott Vermont Professional Quality Vegetable Flower and Urbal Seeds that are 100% organic and non-GMO project verified. On the web, HighMohingSeeds.com. And by White Flower Farm, offering a wide range of carefully selected and expertly grown garden plants.

On the web, whiteflowerfarm.com.

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