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363-The Ethos of the Ecological Gardening Summit, Part II, with Rebecca McMackin

| Care, Podcast

The Ecological Gardening Summit begins Wednesday, May 8, online, at noon Eastern time, and to prepare, I am sharing some of the principles that inspired this inaugural event. This week, I am revisiting my past podcasts with Rebecca McMackin, who will present “Adventures in Ecological Horticulture” during the summit.

Rebecca will join the summit to enlighten us on the importance of creating sustainable habitats for plants, insects, and wildlife. She is a garden designer who holds master’s degrees in both environmental biology and landscape design. She encourages inviting biology into the garden rather than trying to keep it out.  

 

Rebecca McMackin

Rebecca McMackin is the director of horticulture at Brooklyn Bridge Park and a self-described “ecologically obsessed” horticulturist and garden designer.
(Photo Courtesy of Rebecca McMackin)

 

For 11 years, she was the director of horticulture at Brooklyn Bridge Park, an 85-acre New York City public park built on piers originally constructed to accommodate cargo ships but transformed into a wildlife haven in the largest city in the United States.

Rebecca left Brooklyn Bridge Park when she was selected to be a 2023 Loeb Fellow at the Harvard Graduate School of Design. She recently delivered a TED Talk on ecological horticulture and the reasons to let your garden grow wild. 

Brooklyn Bridge Park 

Brooklyn Bridge Park was designed from the outset to be an organically managed wildlife habitat that could be shared with people. The park now boasts more than a decade of research, observation and experimentation on managing land and developing practices to encourage wildlife, and all that knowledge is shared with the public.

“We are all in it for the greater good,” Rebecca says. “We’ve really seen a lot of the things that we’ve experimented with start to bear results. We’ve seen the returns of species that we did not think we would be able to support in this context.”

The strategies that they adopted from others or developed themselves can be used in just about every garden, she says.

 

Brooklyn Bridge Park

Brooklyn Bridge Park was built on obsolete shipping piers. (Photo Courtesy of Rebecca McMackin)

 

What’s at Stake

Rebecca notes that an estimated 16 million people began gardening during the pandemic and says that, more than anything, they want to practice gardening in a useful, meaningful fashion.

“They want to grow food, they want to provide habitat. They want to grow milkweed,” she says. “And so we want to bring them into this movement, share what we’ve learned. And it’s really critical.” 

Ecological gardening is fun and meaningful, and the results are amazing, but this moment on planet Earth is very serious too, she says. “Climate change is obviously massive, but the biodiversity collapse that we are in the midst of right now is catastrophic.”

She cites global estimates that in the last 35 years or so, 45% of arthropods have been lost, as well as one in four birds in the United States.

“This is very, very serious, and it’s terrifying, and it makes a lot of sense that people feel like they can’t make real change in these big, complicated issues,” she says. “And I think that with gardening and ecological horticulture, you can make a difference. You can. It’s a tiny little difference that you can really see. You can see the butterflies come back. You can watch the caterpillars eating the leaves.”

It’s a way for a person to reengage with the idea of creating positive change and not feel helpless and powerless all the time, she says. We have a hand in this.

 

Bird and baby.

The bird population in the United States has shrunk by about 25 percent due to habitat destruction and other factors. (Photo Courtesy of Rebecca McMackin)

 

More than the Classical Organic Gardening Movement

Ecological gardening is not just another term for organic gardening.

“It is gardening that looks beyond the flowers. It looks beyond the plants, and it prioritizes the dynamics among the plants and the wildlife and the soil microorganisms and the people, critically,” Rebecca says. “People are a big part of this process as well. It’s about these relationships among all of the various organisms, and we consider the garden as a system that changes and adapts to conditions over time.”

In traditional horticulture, a gardener would plant a tree, shrubs, Echinacea, etc., and expect them to remain where they were planted. In ecological gardening, gardens are looked at as changing systems that are always in flux and are able to deal with climate change as a result of being dynamic.

“The right plant, right place — you can try and nail it on the first try, but let those plants migrate around and they’ll be happier for it,” Rebecca says.

This work requires looking at the species of wildlife that visit the gardens and observing how they use the garden throughout their lives.  “We research and we experiment and we alter our gardening practices to better support those individuals,” she explains.

Rebecca celebrates the fact that more gardeners are using native plants in their landscapes. “It’s been a long road to get here, but so many gardeners now recognize the importance of doing that,” she says. “But the planting of the plants is really just the first part of that process. The native plants, they’re going to provide food for herbivores and for pollinators that’s so important. But they can also be a lot more than just that. They can be nesting sites, they can be nesting materials, they can be overwintering habitat.”

 

Bridge garden design

Underneath Squibb Bridge at Brooklyn Bridge Park, a garden designed and cared for by Junko Fujimoto.
(Photo Courtesy of Rebecca McMackin)

 

Ecological Gardening Is Catching On

“We care a lot about beauty and the human experience is really paramount here,” Rebecca says. “But you can do both. It is not one or the other.”

The overwhelming majority of the more than 5 million people who visit Brooklyn Bridge Park every year just see a beautiful park, according to Rebecca. They don’t know about the park’s ecological work. 

Raising awareness of ecological gardening as an alternative to traditional gardening is a heavy lift, but getting easier as it catches on.

“Some of the normal processes that you learn as part of a traditional horticultural education, they have to be shifted or even eliminated altogether,” Rebecca says.

Native plants are now for sale at nurseries, the latest research on how to strategically locate milkweed in the garden to better encourage monarch butterflies is readily available on the internet, and apps like iNaturalist make it a cinch to identify any animal or plant. These tools are critical to the work of ecological horticulturists and are accessible to any gardener. 

Connect to the Land and Observe Life Cycles

Botanist Robin Wall Kimmerer says that academic and traditionally Western methods of learning about plants are really about reading what other people have written. The indigenous perspective calls for learning from plants through observation. 

“It is not just better practice from an ecological perspective, but it creates those relationships that people then have with these organisms,” Rebecca says. “Those direct relationships and observations, so you’re not just following a Facebook meme or a certain rote set of instructions that you do every March. You’re connected to the land and to these organisms in a very, very important way.”

For example, when Brooklyn Bridge Park planted smooth aster, a host plant for the pearl crescent butterfly, crews noticed that the caterpillars overwintered at the base of the plant, at the basal rosette. When the caterpillar wakes up in spring, it eats the leaves of the rosette.

“The overwintering part of these animals’ life cycles is really, really critical when you’re trying to get them to take up residency,” Rebecca says.  

 

Butterlfy on plant

A pearl crescent butterfly on its host plant. Ecological gardening involved paying attention to life cycles of beneficial insects to know how to better support them.
(Photo Courtesy of Rebecca McMackin)

 

It’s not enough to just help insects migrate through. There are residential insects that stay year-round when they can find water, food and shelter. 

“It’s mid-June. Do you have flowers blooming for all of your various pollinators?” she says. “It is March. Do you have a duff layer that these animals can be snuggled into to properly over winter? It is April, and you’re doing cutback, and you’ve got these little caterpillars living at the base of your smooth aster. Are you going to step on them? Are you going to rake them out of the garden?”

Traditional gardening practices disturb beneficial insects at pivotal stages of their life cycles. Altering practices in response to life cycles and acting with intention will make a monumental difference in encouraging animals.

“Now when we go in and we do cutback with that little butterfly, we’re very careful around the smooth ast. We make sure not to step on them, and we leave that duff layer there.”

Native bumblebees also live in that duff layer, which Rebecca says is such an important part of a garden for so many reasons. 

“Bumblebees will overwinter there, and often at the base of bunch grasses like Panicum and little bluestem,” she says. 

Because the park employees are conscious of the bumblebee life cycle, they fostered an environment that attracted the state-endangered golden northern bumblebee, Bombus fervidus.

“It’s amazing, right? That a park and that a city is supporting this rare animal, and we want to support it as much as possible,” Rebecca says.

Brooklyn Bridge Park works with entomologists to figure out more about where bumblebees nest, what they need, and how gardeners can provide the resources for them. 

 

Spishbush swallowtail

A spishbush swallowtail caterpillar on Lindera.
(Photo Courtesy of Rebecca McMackin)

 

Cut Back on Cutback

Cutting back bunch grasses is necessary to ensure they don’t rot, but they don’t need to be cut back all the way to the ground, Rebecca notes. 

“Generally, during cutback, we like to leave as much organic material on the ground as humanly possible,” she adds. “But with grasses, there’s a number of reasons why we don’t do that. One is that we need to keep the soil as lean as we can because the grasses don’t like a lot of organic matter. But the other one is that they’re a fire hazard.”

Cutback is not a natural process — it’s a human practice, Rebecca says. 

She credits Piet Oudolf, the designer of the High Line in Manhattan and a leading figure in the New Perennial Movement, with calling attention to the beauty and form that seedheads add to the garden in winter. Many gardeners have refrained from cutting back in fall, delaying the work until spring, and this has benefitted overwintering insects as well as birds, which use those seed heads as a food source all winter. 

Rebecca encourages gardeners to think about where in their garden beds or on their properties where they can incorporate these practices.

“An incredible amount of the habitat that our gardens provide are from the structure that gets cut out, cut back,” she says. 

From a beetle’s or ant’s perspective, a small garden is like a jungle, and the forest of stems, twigs and leaves provides overwintering habitat. When gardeners remove that duff layer before winter, insects have no place to survive the winter. They won’t be around in spring when birds look for insects to feed their offspring.

The duff layer is also a heat insulator that protects plants on the edge of their hardiness zones. The area between the ground and the bottom of the snowpack is called the subnivean zone, and it never gets below freezing temperatures. “It’s like a down comforter that is literally covering everything,” Rebecca says. 

During cutback, if you take the time to look, you’ll notice which stems are full of pith and which are hollow. Hollow stems that are at least an 8th inch in diameter provide habitat for stem-nesting bees.

Pollinator conservationist Heather Holm, who has been a repeat podcast guest, advises leaving at least 18 inches of the stems standing, so what remains can provide habitat for stem-nesters. Heather calls this “garden stubble.”

“It’s a cool look,” Rebecca says. “I think it looks better than a clear cut.”

Brooklyn Bridge Park staff are always considering where they don’t have to cut back or where they can cut back less because when it comes to providing habitat for insects, less cutback is more. It also creates winter interest for the human eye.

Birds won’t nest where it’s been cut back every year and where they see humans go. Brooklyn Bridge Park identifies areas where no one will go, so the birds are comfortable setting up nests and rearing young. 

“It really speaks to how much of the gardener’s work is disturbance and how much habitat can be encouraged just by letting things be,” Rebecca says. 

Less disturbance and less meddling will lead to better ecological results. 

“This inclination to micromanage is not actually healthy,” Rebecca says. “It can actually be harmful.”

 

Cutting grasses

Christina Severin cutting back grasses at Brooklyn Bridge Park. Grasses can pose a fire hazard if not cut back.
(Photo Courtesy of Rebecca McMackin)

 

 

Know What You Are Weeding Out

The staff weed out invasive plants at Brooklyn Bridge Park, and they have a rule that no one can weed out a plant unless they can identify what it is. Sometimes they work to ID a plant only to discover that it is a rarely seen native plant. For instance, they found an endangered sedge, and instead of pulling it, they encouraged it to grow and spread, distributing the seeds around the park. They also migrated a state-threatened salt marsh aster that showed up to a marshy area, where it is now thriving. 

Leave Organic Matter on the Ground

Leaving the leaves is a major,” Rebecca says. “I’m so glad that that is such a popular phrase that is out there now.”

People have this sense that deciduous trees are throwing their leaves away, she says. But in reality, trees are carefully placing their leaves over their root systems where they can act as insulation over the winter. And then the nutrients in those leaves go right back into the tree itself and create the soil for the tree. 

“A lot of gardeners have it backwards,” she says. “We think we’re creating the soil for the plants, and they are the ones who are creating it for us.”

 

shrub

In nature, no one rakes up the leaves. Leaves insulate soil in winter and break down the following year to build soil. (Photo Courtesy of Rebecca McMackin)

 

Let Nature Do Its Work

A plant alone in a garden with nothing else is a resource of herbivores and may be targeted and overwhelmed by a herbivorous pest, such as aphids. But when there is a wide variety of plants, densely planted, pest pressure is spread around, and plants can better shrug off damage.

Having a variety of plants also brings in more predatory insects that target pests, naturally keeping those pest populations under control.

“The problem with traditional horticulture is that we keep wiping out the herbivores,” Rebecca says. Before the predators can take care of an infestation, gardeners have already applied a pesticide.

“We’re wiping out the populations of all of the beneficials that keep those animals in check, and it’s this cycle that never lets things get in balance,” she says.

Brooklyn Bridge Park demonstrated how to break this cycle. The park allowed, for years, aphids to prey on catalpa trees. After a couple of years of refraining from using pesticides to control aphids, the rare two-spotted ladybeetle arrived, and it preyed on the aphids that prefer catalpa trees. Nature provided natural pest control.

This Work Is Critical in Cities

“Half of humanity currently lives in cities and that number is rising,” Rebecca says. “People are migrating to cities all over the entire planet.”

The world population is expected to reach 9.7 billion people by 2050, and by then, 75% of people will live in cities.

“We must figure out ways to gracefully incorporate quality wildlife habitat into cities. It is absolutely critical if we want to be able to support wildlife and biodiversity on this planet,” Rebecca says.

 

Leafcutter bee

Plants treated with system insecticides can kill pests as well as beneficial insects like this leafcutter bee. (Photo Courtesy of Rebecca McMackin)

 

The Ecological Gardening Summit, which will run from noon to 4:30 p.m. Eastern, will feature talks from entomologist Dr. Doug Tallamy of the University of Delaware, pollinator conservationist Emily May of the Xerces Society and Garden for Wildlife manager Mary Phillips of the National Wildlife Federation in addition to Rebecca McMackin. I hope you will join us!

If you haven’t listened yet to my conversation with Rebecca McMackin on ecological gardening, you can do so now by clicking the Play button on the green bar near the top of this post.

How has ecological gardening provided a more inviting space for wildlife in your garden? Let us know in the comments below. 

Links & Resources

Some product links in this guide are affiliate links. See full disclosure below.

Episode 134: Bird Population Decline and What Gardeners Can Do to Help

Episode 232: Ecological Horticulture at Brooklyn Bridge Park, with Rebecca McMackin, Part I

Episode 233: Ecological Horticulture at Brooklyn Bridge Park, with Rebecca McMackin, Part II

Episode 237: Ecological Gardening: Creating Beauty & Biodiversity

Episode 331: The Ecological Garden Blueprint: 10 Essential Steps That Matter Most 

Episode 362: The Ethos of the Ecological Gardening Summit, with Doug Tallamy

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Rebecca McMackin on Twitter: @McmackinRebecca

Let Your Garden Grow Wild | Rebecca McMackin | TED

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About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

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