I WATCHED A ZOOM lecture the other day that really put into words a lot of the ways my own deepening understanding of ecology is shaking up the way I practice horticulture—from spring cleanup, right on to the last chore of the active year.
The lecturer was Rebecca McMackin, director of horticulture for Brooklyn Bridge Park in New York City, where she leads the team that manages 85 acres of diverse parkland with a central focus on habitat creation of woodlands, wetlands, and meadows to build soils and support birds, butterflies, and other organisms.
We talked about the dynamic tactics they use and when and why–a whole different approach to spring cleanup, and why the staff lets the life cycles of animals (from insects on up) dictate what happens when, garden maintenance-wise. Like why some things don’t get cut back, and others that are still seed-laden when they do have their seeds collected and set aside (photo above), then returned to the spot after whatever cleanup is needed there.
Rebecca (follow her on Instagram) has worked at Brooklyn Bridge Park for over a decade. She has two master’s degrees, in landscape design and in biology, and has served on the board of the Ecological Landscape Alliance, and is currently vice president of Metro Hort Group, a professional organization in the city.
Read along as you listen to the April 26, 2021 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).
ecological landscaping, with rebecca mcmackin
Margaret: What a great lecture you gave that I watched the other day. So just to start for perspective, context, etc., this 85-acre Brooklyn Bridge Park, which more than 5 million people visit a year, I think you said, isn’t exactly like my backyard—and it isn’t exactly like a rolling park of 85 contiguous acres of grassland, either. So tell us about what it is.
Rebecca: So Brooklyn Bridge Park [part of it can be seen below] is this massive public park in the middle of the largest city in the country. It’s built on reclaimed shipping piers. So an incredible amount of material, a bunch of it recycled and reclaimed, was shipped in and used to build the hills and the meadows and the lawns and the soccer fields.
It’s just a massive construction project that, after building for a solid decade, we are planning to finish this fall. It was designed by Michael van Valkenburgh Associates, and it was always intended to be organically managed, but in addition to that, they designed in salt marshes and these thickets that provide habitat for birds, and a giant native wildflower meadow that we call the Flower Field.
So we, the Brooklyn Bridge Park horticulture team, we inherited this marvelous canvas. We have over 16 acres of just garden bed that doesn’t include lawn, even that’s just garden-bed space. And we manage that space as wildlife habitat.
In order to do that, we practice ecological horticulture, which is organic, but it’s actually pretty different from organic gardening.
Margaret: And I definitely want to drill into that, because that was one of the things that I don’t think everybody’s heard that. Because a lot of my listeners hear me talk about organic and also talk about native plants and about habitat-style gardening and so forth. But this idea, this phrase “ecological landscaping,” can you explain how that’s organic-plus or native-plus or whatever [laughter]?
Rebecca: Absolutely. So it’s very similar, right? It’s organic in its practices, but I think it goes beyond that. It’s a form of gardening in which the goal is to create and manage gardens as wildlife habitat for key species. We work a lot with plants—obviously, we’re gardeners. But it’s animal-centric, and it really focuses on the dynamics that exist between and among the organisms in our garden.
So, if you buy Echinacea from a box store and that has been pumped full of systemic insecticides, and surround it with a foot of wood chips, that plant is more like an animal in the zoo.
In order for it to really function ecologically, it needs to form those relationships with pollinators and caterpillars and soil microorganisms, and we’re trying hard to encourage those dynamics. And in order to do that, we practice a lot of the management strategies that are thankfully very well-known now, like leaving seedheads up over the winter and cutting hollow stems to 18 inches for stem-nesting bees. [Above, Brooklyn Bridge Park gardener John Ford with a katydid.]
Margaret: So you just mentioned buying an Echinacea at the big box store, and I loved one of the lines in your talk the other day. It said something like, “It’s so hard to find a butterfly host plant to buy that won’t kill your butterflies.” Just drill into that for a second. Just so people know what to ask for when they’re shopping this spring, what to ask about.
Rebecca: Absolutely. Absolutely. So for those of us who are seeking to do this work, it is absolutely tragic how difficult it is to do, I think. Although the industry is really changing, and people and nurseries, especially, are responding to demands. So plants that have been treated with systemic insecticides like neonics, when you plant them, and if that plant is a butterfly host plant, that plant is going to kill your butterflies when they come and visit it. And so when we plant our butterfly host plants, we make sure we check with the nurseries, we make sure that they haven’t been treated with things that can harm the animals.
Now, I know that many native plant nurseries are starting to pay attention to this. You can even find plants in box stores that may claim not to have been treated, which is all wonderful. But it’s really important to, when you do buy plants, advocate for and really check in and make sure that those plants haven’t been treated.
Margaret: Right, and you said, systemic—these are systemic, the neonicotinoids. Meaning even if the leaf falls off that was sprayed, the plant has ingested and metabolized this substance and will still poison, right? So it’s not just like a surface thing that if I bite on that surface, I get sick or die.
Rebecca: Exactly. It can’t be washed off, and it persists, right? It persists in the landscape. There’s evidence that it can persist in the soil. So it’s not part of planting a garden that is going to function ecologically. [Photo above by Etienne Frossard.]
Margaret: Right. And we definitely can, as the consumers, we have the ability to go and ask at the counter, every time we go in, and this is adding up to pressure on the industry. So that’s really positive to sort of speak with your dollars and your voice, literally, at the garden centers.
Margaret: Yeah. Yeah. So you think in these sort of systems, ecological systems, and also, as you just mentioned, you think about particular organisms, particular animals—whether insects or birds or whatever. So let’s just do a couple of examples of those that came to life in the presentation that I watched.
I think you used the example, for instance, the common and wonderful little pearl crescent butterfly, for instance. How do you make someone like that happy [laughter], or birds that nest on the ground? These are the cues that help you and your garden team determine what to do and when to do it.
So tell me, Rebecca, tell me about some of the cutback strategies and how learning about these animals informs when you do, how much you do, how severe, etc.
Rebecca: Absolutely. So a big part of cutback is timing for us. Originally, we started doing cutback very early so that we didn’t compact the soil while it was wet. And then we started doing it very late, so we would let migrating birds migrate through the park before we did cutback.
And now it’s really reached a level that I think is wonderful, where our cutback timing is based on the behavior of the birds themselves, and we work with our local park birder, to tell us about when certain migratory species are using certain areas of the park and how they’re using them. Are they doing mating behavior that might be very special, and we should stay out of that area?
And our cutback strategy is really based around the relationships we have with those animals, as opposed to any hard-and-fast rules. And we try to develop protocols for people, as well. We do try and create things that people can follow. But I think the most wonderful part of this work is when it really forms the relationship between animals and the people that care for the landscape and the plants themselves. When our garden practices are really based around the behavior of those animals.
Margaret: Right. I think you have some areas that are sedges—a popular plant at the moment. More people are learning about the Carex, the native Carex species as sort of groundcover, “lawn alternatives,” all these phrases that we use about them. You don’t mow them [laughter]. In nature, they don’t get mown [below]. So they’re not grass, even if we’re using them as a “lawn alternative.” Right?
So use that as an example. You’re kind of trying to get us to look differently at those sort of mounds of last year’s Carex, or something left in place. Is that the case?
Rebecca: Absolutely. A lot of the work that we do centers around just leaving things alone. How can we get out of the way of the natural processes that are happening in our gardens and just let them do what they want to do? We’re not under the impression that we can improve upon any of those processes.
And so with things like Carex, and even many other plants, we don’t actually need to cut them back. And we’ve realized that they actually look much better when they are not being cut back. It’s a much more beautiful, natural feel, and that’s really important. A big part of our job is not only developing the practices that encourage wildlife, but changing the acceptable aesthetics around gardens, so that people feel more comfortable having these gardens that are really functional for wildlife, as well.
Margaret: Yes. And I think for me, and I’m a much older gardener, and so I was taught this sort of hand-me-down wisdom of this that came mostly from English garden books. Let’s be honest; that’s how Americans of my generation and older, that’s what we were inspired by, and it’s tidy, and it’s you clean up just within an inch of its life [laughter]. You know what I mean? It’s a little obsessive. You want to be ready for spring, so you would never leave any leaf litter on top of where your minor bulbs are and so on and so forth because it’s guided by this aesthetic that’s a little bit perfect.
And this is a very different thing. You’re trying to normalize a different aesthetic, I think.
Rebecca: Absolutely. And it works in our park. It’s absolutely beautiful, and it works in our park. We have certain areas that we keep a little bit more formal and we do use traditional mulch in order to cover the ground. And those are our park entrances; they welcome people into the park with a very familiar aesthetic. And then once we’re inside, we’re allowed to use this really more naturalistic look.
And it’s important that that area be kept just slightly more formal. One of the things we do is put a nice mulch edge on the front, keep it a clean edge, what Mt. Cuba Center calls “a cue to care,” to let people know that it’s not neglected; it is intentional. And then that allows for a bit of benign neglect in the back.
Margaret: Yeah. So I’m very envious, by the way, that you said you were almost done with cutback because up here a couple of hours to the north, Margaret is not quite anywhere near done [laughter]. So I’m out there cutting things back, and take me through it. Take me through, I’m looking at a plant, and I’m about to apply my pruners at a certain level. Take me through how Rebecca looks at it, and what she does with the seedheads, if there’s still some seeds and kind of what the process is.
Rebecca: Sure. So the way to approach it is to sort of think, why am I doing this practice? What is necessary about it? Can I just not do it? And if you do need to do it for aesthetic, or if it’s a bunchgrass and it’ll rot, if you leave too much organic matter on it, then you do go ahead and you move forward with cutback.
Even with cutback, we’re trying to leave as much of that material on the ground as possible. So that, as you mentioned, we’re not creating just a flat ground layer of mulch that doesn’t really function as habitat. We’re creating a diverse duff layer for beetles and ants, and it’s a micro-wildlife environment on the ground.
And so when we do cutback, at first we’ll cut the seed heads off of any plants that have viable seed heads. So asters, and penstemon in the spring, we’ll put those in a bucket [photo, top of page] and then go ahead and cut down the rest of the material often in 6-inch chunks. So that that material can then just go straight onto the ground and doesn’t get cleaned out and raked out. And nothing has to go back in, right? Everything that the plant produces is staying in that environment as the plant intended, right? We’re trying to mimic those natural processes.
Plants don’t plan to get cut back in the spring. They want to grow in a soil mixture made up of the organic matter that they leave behind. And so we’re trying to encourage that. Then after we’ve done the cutback, we will often go in and put those seed heads back into the landscape. And so that any birds that would like to eat the seeds have them available, and then they also do the job of seeding in, as well.
Margaret: I loved what you just said about, and I’m not going to be able to repeat it exactly, but that the plants are growing in the soil that they kind of help—with their debris and so forth—they help create that soil. They help kind of dictate the character of that soil. And in the lecture I watched, you had an example of maybe it was a juniper and the idea that the soil beneath the Juniper…
And we should explain to people, as you said a little bit briefly at the beginning, I mean, it’s not like this land was there. This is created, and you’re creating and bringing in material that’s becoming soil, but the plants are helping you build the soil that they like beneath themselves. Aren’t they? Could you give us that juniper example.
Rebecca: Absolutely. So I think a lot of gardeners are under the impression that we’re making the soil for plants, and that’s not really the way that it works. The plants are making the soils for themselves, and then for everybody else, including us. In our park, we have engineered soils that were brought on site. They were mixed. And so a big part of our job is taking those soils and turning them into real soil.
But even in a garden that is on the edge of a woodland, this work is still really importan, because this is how plants and animals together make soils. A lot of people are under the impression that a herbaceous perennial or a deciduous tree is throwing its leaves away in the fall, that they’re just getting rid of them. And what they’re really doing is placing them down on the ground, right over their root system, where they get reincorporated into the soil.
They act as a natural mulch. They feed the soil the nutrients that attract the organisms that cycles those nutrients, and then can create the soil again for the plant.
It’s like a slow-motion carbon fountain, with that material falling from the plant, getting incorporated in the soil, going back into the trees themselves and other plants. And then that whole thing happening over and over again. So as much as possible, we try to replicate that system.
The way that you see that in junipers, is that it’s an early successional plant, right? It’ll grow in the middle of a meadow. And as we know, meadows often have high-pH, bacterially dominated soils and a forest, or in this region, generally has a lower, more acidic soil. And the Junipers will march right out into the meadow [laughter], and they will use their needle castings and their root exudates to lower the pH of the soil that they’re growing in.
So if you dig a hole right underneath the juniper in a meadow, you’re going to find soils that are orders of magnitude lower [pH] than the soils maybe even just 10 feet away because that plant is literally terraforming the soil, in order to create an environment that it wants to live in. And then that allows the forest to move in.
And so we try to get out of the way of that process. We try and research those processes and then let the plants go ahead and do them. And when we go in and we rake out all of those leaves, when we’ve stirred the soils over and over again, we’re interrupting those processes. And our job is just trying to figure out, again, really just how we can let them happen in a healthy way.
Margaret: Right. And I don’t know if you’ve seen Doug Tallamy’s new book, “The Nature of Oaks,” that just came out a couple of weeks ago, but boy, oh boy. I mean, if one message comes through, using oaks as the example, it’s leaf litter, leaf litter, leaf litter—that this is the most powerful… The example you were just using and the example of oaks—this is where the action is. And so much critical life, food-web-supporting life is going on in that leaf-litter level. And so, so important to be hands-off where we can.
Rebecca: Yeah, and it requires nuance. You can’t plant a very small, delicate, anemone underneath an oak tree and walk away when it’s covered in a foot of leaves, right? You still need to do the job of making sure that your soils can process those leaves. That mats are not being formed on top of our plants. And so we do remove leaves, especially if they have diseases. We’ll map those areas and remove leaves underneath, Aesculus or London planes or sycamores that might get foliar diseases. We will do that, and we do remove leaves, but wherever we can, we absolutely try and leave those leaves in the landscape.
Margaret: Right. I love the example of the sort of chunking, as I’m cutting back, not cutting at the bottom and having this 3-foot thing or 2-foot thing or whatever. And then I’m going to put it in my basket to carry away or my wheelbarrow or whatever, my tarp. But I’m chunking it into the 6-inch increments and it’s then able to fall on the ground and just be there and bringing the seeds back and so forth.
Now, you mentioned early on, just quite really briefly, you mentioned pithy stems, I think, sort of stems that certain types of bees can use and so forth. Can you give me some examples of those?
Rebecca: Sure. So again, a lot of asters do that really well, and plants in Asteraceae, like Vernonia, have perfect stems, like Rudbeckia. We’ve also seen really good stems on Penstemon that provide great habitat for stem-nesting bees. And those stems, you really need to leave them up. A lot of people will leave them up for a little while and then cut them back, but the goal here is really just leaving them up year after year so that the bees can use them to overwinter.
Margaret: Yeah, elderberry, I think is another—among woody plants, elderberry has those types of inviting stems for stem nesters, too. So it’s like don’t clean them up too early because they tend to get some dead wood at the tips and so forth. Don’t clean them up too early.
Margaret: So, I definitely want you to come back later in the season to talk about rethinking sort of fall and winter cultural tactics, but as a sort of sneak preview, you said you try to leave leaves where you can and so forth. Are there other things as the season progresses or as the season gets later, toward the end, any other key highlights of sort of how ecological landscaping is different from ornamental horticulture practices?
Rebecca: Absolutely. I mean, I think a big part of the way that we encourage biodiversity is our pest-management strategy in the landscape, which is rather than seeking to maintain a sterile environment, we try and build up the biodiversity that can kind of keep everything in balance. And so when you plant a plant, you’ve really created a vacuum. You’re going to get a bunch of herbivores, right? There’s nobody eating that plant, and so those herbivores are going to move in. And if you, the organic gardener, consistently wipe away aphids, for instance, even if you’re using organic practices, like horticultural oils, what you are doing is knocking back the population of the herbivores so that the populations of predators don’t have a chance to build up.
We will leave big population of herbivores so that those predators can build up their populations, and then keep those herbivores in check themselves. A lot of people when they go in and they wipe out aphids, for instance, they’re also wiping out many of the predators that are balancing those pests in our garden.
Margaret: Right. So if you interrupt the food chain, you hurt the organisms at each higher level. I mean, you’re taking away the food.
Rebecca: Exactly, and you’re in a situation that you must constantly interfere with, right. You’re creating so much work for yourself, instead of just letting these processes balance themselves out.
Margaret: I think you’re going to be adding some more of this kind of information to your website. You’re helping to do more education and add more information to the website. Yes?
Rebecca: Absolutely. So a big part of our work now is advocating for these sorts of strategies. And we are going to be putting a lot of information starting tomorrow on Earth Day. We’re going to be putting a lot of this information on the website. So we’re slowly rolling out fantastic details on native plants that thrive in cities, as well as their ecological functionality, as well as some of our databases that we’ve created around weed management, which bees are in the park, for instance. So all of that’s going to be up on our website soon.
Margaret: O.K. I mean, this is what really struck me. If people are wanting to know, does this stuff work [laughter]? This shift in practices and attention and so forth. You have 170 species of birds, as I understand, that have visited or visit the park. Now, I mean, there was no park, there was no land, there was no habitat—and they found you. And so to me, that’s like, “Yep, it works.” [Laughter.] [Monarda photo above by Pawel Pieluszynski.]
Rebecca: We’ve seen those practices really work on the ground level as well with key species, like with, as you mentioned earlier, the pearl crescent butterfly. That’s a butterfly that overwinters as a caterpillar underneath the basal rosette of the smooth aster that is its host plant. And so in the spring, those caterpillars emerge and start to eat the plant.
And when we do our cutback strategy, we pay special attention not to step on those plants and to make sure we’re kind of treating that area carefully. And as a direct result of that, we’ve seen just huge populations of pearl crescents in the park. So we can see it, especially with that host plant-butterfly dynamic, the effects of your gardening practices are right there. They’re right in front of your face. So it feels really good to help those dynamics and populations in that way.
Margaret: Well, Rebecca McMackin from Brooklyn Bridge Park, I can tell that we’re going to have lots more conversations. So thank you for getting us started, and thanks for just inspiring me. I really appreciate it. I’ll talk to you soon again.
more about ecological landscaping & brooklyn bridge park
- Brooklyn Bridge Park horticulture resources to explore
- Learn more about the park’s plants
- The overall park website
- Follow Rebecca McMackin on Instagram
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the April 26, 2021 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).