PERSPECTIVES 01: Clones Zones and Migrants

This fall, landscape designer and researcher Leah Kahler joined the Weitzman faculty as the 2024-2025 McHarg Fellow. Through multi-sited fieldwork and archival research at the National Agricultural Library, Leah’s work at the McHarg Center documented the expansive socio-ecological geographies of the plant nursery trade. Her research asks how the design and horticultural trades might find new methods for plant selection and sourcing. Kahler’s work reveals the labor and environmental processes that precede a plants’ arrival on a jobsite, re-framing the $13.8-billion US tree and seed nursery industry as an important agent in the material culture of the American built environment. In the spring, Leah taught a graduate-level seminar called “Clones, Zones, and Migrants,” based on her nursery research. This course explored plant migration across cultures and climates, as well as the labor and environmental implications of plant procurement. Through ongoing engagement with professionals and academics, Kahler is encouraging current and future landscape practitioners to reconsider assumptions around the sustainability of landscape construction, “native” planting, and asking how these practices might better align with the field’s aspirations to environmental justice. 

Following her culminating lecture titled, “Before a Plant Arrives on Site: Politics, Migrations, and Possibilities of the Plant Nursery Trade,” Leah sat down with one of the students in the seminar, Nitya Patel (MLA ’25) to reflect on the fellowship year. 

Nitya Patel To start us off, could you introduce yourself, extending beyond your fellowship year?

Leah Kahler I'm a landscape designer and researcher, native of southern Louisiana and born in Baton Rouge. I grew up less than a mile from the Mississippi River, near the mouth of one of the largest watersheds in the world. This meant that landscape and its incredible, sometimes terrifying, dynamism was present in my life from the very beginning. It’s almost impossible to grow up in southern Louisiana without fascination and respect for the way that ever-changing landscapes shape almost every aspect of our lives in the Gulf; from floodplain agriculture that’s (sometimes) kept dry by the river’s levees, to the increasingly prevalent pluvial floods. It’s a place where the idea of nature and culture as separate is actually inconceivable, because the landscapes are so highly modified through engineering and design practices.

My roots in southern Louisiana also meant that I was more familiar with the productive and extractive landscapes at the heart of today’s petrochemical industry (on former plantation land) than designed parks or gardens. That early understanding of extractive landscapes and the ongoing fight for environmental justice across the region have informed my research agenda, which seeks to trace the often-invisible geographies of production and consumption in the built environment.

My undergraduate degrees are in Anthropology and Growth and Structure of Cities, which I think has made me strive towards being sensitive to sites in all their complexity. I still approach any research project like an ethnographer, walking with people on site, strive for deep listening, and with enthusiasm for the relationships between material conditions past and present.

NP When did you first become curious about the questions that now drive your work—was there a landscape or an experience that planted the seed?

LK Ha, funny story. I first realized I was interested in landscape during an undergraduate semester abroad in Morocco—when I was studying transnational migration. In my free time, I found myself walking around centuries-old gardens and cemeteries and became curious about them— about how large, regional-scale water infrastructures underpinned the beautiful fruit and floral gardens and cemeteries that I returned to week after week. I became really interested in the intersection of memory, history, and garden making. So when I went back to my college after that experience, I found myself reading all these books about Islamic gardens, and then literally in the library—this is the importance of actual book stacks in the library— next to the books about Islamic gardens, I found books by landscape designers and historians. It all sort of snow-balled from there.

My research documents the ways in which large-scale industrial production of plant material resembles concrete production more than we might realize

The specific research that I'm doing right now on the nursery trade draws on questions that first arose during my time in design practice. The tagging trip to the nursery is a rare instance in which landscape designers visit the sites of production. Given my upbringing and interest in the often-concealed places that produce the materials for the built environment, these trips inspired curiosity about the nursery industry. Who grows plants before they arrive on site? Where are they grown and what does that mean for their ability to adapt to shifting climates? Jane Hutton’s 2019 book Reciprocal Landscapes inspired me to think about how the material and social implications of our work as landscape architects defy neat site boundaries. The research and teaching opportunities of the McHarg Fellowship allowed me to dig deeper into questions about the movement of plants and people that tend them before they arrive at the job site.

NP What are some of the biggest misconceptions about the nursery trade that your work is looking to disrupt? 

LK The first misconception that comes to mind is the idea that “green” is categorically and unequivocally good. There is a growing understanding in our discipline that materials like concrete, steel, wood, even stone are the result of extractive processes that rely on cheap, vulnerable labor. On the other hand, planting or plant-based materials are often billed as a feel-good, morally superior antidote to those other, supposedly more extractive material processes that come at high environmental, labor, and energetic costs.

My research documents the ways in which large-scale industrial production of plant material resembles concrete production more than we might realize, as well as case studies for growing otherwise. For example, a street tree installed here in Philadelphia might travel more than four thousand miles by freight before reaching a home on our sidewalks, all in the name of mitigating the urban heat island effect and creating opportunities for shade in the city.

The second widely held belief that I’ve been chewing on is one that you all were all asked to engage with in in the seminar: how does the construction of native plants operate for landscape designers? Let’s take the Philadelphia Street tree as an example. That plant may be native, but it’s not local in any sense. That’s why we worked as a class to develop more nuanced language about the relationship between plants, their places of origin, and what that means in terms of socioecological belonging. 

NP That’s a great segway into the seminar that you taught in Spring 2025—what were some of your pedagogical priorities?

LK As you probably remember, the class’s title, “Clones, Zones, and Migrants” is also its structure. In the first unit, “Clones” we look at the existing practices of the nursery industry and hear from growers about all that it takes to bring plants to the market and to the job site. The second unit called “Zones”  asked students to zoom out in scale and document the planetary movement of a particular plant that is meaningful to each of you. This unit documented how the plant was moved by human hands through processes tied to empire building, moved according to climate shifts or in response to trends in the global plant trade. The last section, called “Migrants,” looks at the guest worker programs that underpin the industrial horticultural model, and debates about assisted migration of plant material. The last exercise gives students the opportunity to design a reciprocal network of plant cultivation, production, and planting that refuses the abstraction of the faraway nursery landscape.

Throughout the semester, we hear from scholars in the environmental humanities, landscape history, and literature, as well nursery growers, public gardeners, federally employed urban foresters, and landscape architects who have ventured out beyond the traditional off-the-shelf model of planting.

There’s a real need for thinking with more complexity and through the plants’ own agency, beyond the “Native is good. Non-native is bad” dichotomy.

I wanted the class to offer a sense of breadth in terms of disciplinary points of view and methodologies. One of the most amazing things about landscape design, with all of its dynamic, living materials, is that no single way of knowing can ever really complete the picture. For example, the more you know about plants from an ecological point of view, the more you wonder why we call certain species invasive and others native.

Another priority is to teach design research methods with rigor and fidelity. Drawing and making is certainly a part of design research, but I put real emphasis on citations for all the source material that you all used to support your drawings and design proposals. 

NP What were some of the most surprising or meaningful directions the students took in their projects?

LK Well, one of my favorite moments of the seminar was when you came into class after a deep dive on how marigolds got to India by way of Portugal and Meso-America. You were so surprised and excited to learn that marigolds are not actually native to India. Despite the fact that they are ubiquitous in auspicious events, they are actually a replacement for native Calendula. You told some incredible stories about the plants’ mistaken identity and were looking into centuries-old paintings trying to find when the Calendula became the marigold. The question that your drawing poses, “How would marigolds see the world?” is such a great one, because it really centers the plant’s own logic rather than the humans who have ascribed value to it.

NP Honestly, when I began researching marigolds, I didn’t expect it to resonate so much. I was just following this curiosity about something that felt so familiar and unquestioned in my culture. Your encouragement helped me feel like I could really follow that thread.

Learning that marigolds aren’t native to India was a moment of surprise, but not in a disappointing way. It made me think about how fluid cultural memory can be. Something so central to our rituals and everyday life can, in fact, have come from somewhere else entirely, and yet be completely naturalized over time. It made me reflect on how culture is built not just on origin, but on relationships, repetition, and care.

What really shifted for me during this project was how I began to question the stories we inherit about plants, about history, about identity. Who tells these stories? From what perspective? That’s why I loved asking, “How would marigolds see the world?” because it flipped the script. It asked me to step out of a human-centered narrative and instead try to imagine a plant’s perspective: its journey, its adaptations, its unintended meanings across time and place.

I want to keep exploring how plants move with people, how their meanings shift, and what we might learn if we try to see them as participants in history, not just background or decoration.

LK I was also delighted with how much energy and knowledge the two students from the Fine Arts and Architecture departments—Jingyi Ling and Holly Smithberger—brought into the course. Jingyi’s incredible map was made with honey that shows the landscapes where Honeysuckle has grown, with darker areas where it is considered native and lighter where it is deemed invasive. And Holly’s research about the development of greenhouse architecture in the 19^th century was such an excellent contribution to the class during the “Clones” section. 

Oh, and last one, it was such a delight to see Ryan Drake—Natural Areas Manager at Morris Arboretum—respond to Andie Kennedy’s final project. He proposed a network of sites from Virginia Beach to Boston that share seeds for assisted migration of plant material as our cities warm. During our showcase Ryan told Andie that his idea wasn’t so far-fetched, that he and others at the Morris are engaged in a multi-sited research project that has collected Quercus virginiana seed from its northern-most range in coastal Virginia and trails their growth here on Penn’s campus. Apparently, the Live Oaks are doing well, with no frost damage over the winter. So yes, constant surprises! 

NP I am curious about the audience for your research, Leah. Who do you think, or who do you hope, will be most impacted by your research: practitioners, policy makers, communities, nurseries, students, or some other group altogether? 

LK The short answer is that audiences will depend depending on the outlet. The lecture I delivered last week was geared towards you all, the Weitzman students, to introduce you to a way of thinking about the material choices, implications, and vast geographies that the process of making landscapes affects. The lecture also gave a window into the larger histories of plant movement and federal legislation that decide which plants belong and which do not, according to their places of origin. Future publications will be geared towards other scholars and practitioners, depending on the publication. I’m lecturing over the summer at landscape architecture offices that are interested in the alternative growing models I showed during the lecture and possibilities for integrating them into their professional work. So the audience is quite varied.

NP Before we wrap up, I want to return to your experience here at Penn and the McHarg Fellowship itself. Could you reflect on how mentorship from Weitzman faculty has shaped your fellowship year?

LK For one, teaching with Sean Burkholder and Azzurra Cox in the first semester studio was a great way to start the fellowship because you’re very much part of a team, and there’s built in support for all the small but important start-up questions that you need to get the ball rolling at a new institution.

Presenting updates of my research to the McHarg board and to the department faculty gave me the chance to get helpful feedback while the work was still underway, and their support was essential while I was searching for what would come next after the fellowship year. I was on the academic job market this year and some of the faculty were generous enough to sit through my job talk before I did on campus interviews and give feedback and pointers from what must have been decades of collective experience.

NP Let’s talk about the way forward. If someone were to build on your research, what do you think are the next steps or next questions? For example, I’m thinking about this system in the context of India, where I’m from.

LK Exciting! My work is based in the North American supply chain, which of course has planetary reach and uses plant material from all over the globe. But my sense is that the pathways to plant production here in the US and Canada are extremely formalized compared to the rest of the world. You’ve described the process of landscape construction in India as being less rigid than here in the US and I’d be curious about what that means for the process of plant procurement. Where do plants come from? How far do they travel? Who grows them? And what does all of that mean for the ecological provenance of planted projects and the labor required to grow them?

For example, if plants used in designed landscapes are collected from seed close to their destination sites, the inherent climatic intelligence of the plants is not lost in the same way that it is here when we’re talking about industrial horticulture. In my own work moving forward, I’m looking forward to documenting other modes of growing based in care and repair with some of these same questions. I look forward to hearing or reading what you find out.

NP Absolutely. What stood out to me in your research is how formalized and traceable the North American plant supply chain is, which allows for a certain kind of analysis and intervention. In contrast, in India, much of the nursery and plant trade operates informally from small roadside vendors to larger but still undocumented networks. This makes it harder to trace, but also reveals a different logic of care, distribution, and ecological attunement that isn’t captured in formal systems. I see a lot of potential in studying these informal ecologies; how they function, who maintains them, and what we can learn from them as alternative models of plant production and landscape construction.

I want to wrap it up with a final question – Is there a question you wish people would ask you more often, or one that wish people would ask Landscape Architects more often?

LK I wish landscape architects would ask “Is this landscape architecture?” less and start asking “Who else needs to be here? Whose voice is missing from this research, plan, or process?”

NP Thank you so much Leah for taking time for this interview and sharing more about your work the development of this seminar. 

This interview was conducted for Perspectives 01, Fall 2025 and has been edited and condensed for clarity.

Leah Kahler is a landscape designer and researcher whose work is motivated by justice-oriented storytelling though the lens of landscape. Her research explores the socioecological legacies of the plantation landscape, focused on sites of labor, extraction, and production in the American south.

Nitya Patel (MLA ’25) is an urban designer and landscape architecture student fascinated by the messy entanglement of socio-political dynamics and ecology in rapidly urbanizing cities. At the University of Pennsylvania, she explores the idea of landscape and urbanism across disciplines and borders.