In a Spring 2025 course led by 2024-2025 McHarg Fellow Leah Kahler, students explored the movement of plants across cultures and climates, as well as the relationships between recreational and productive landscapes.
Nitya Patel, a second-year Master of Landscape Architecture student, chose marigolds as her subject for Kahler's assignment. The flowers are “used extensively in India for every happy or sad event,” Patel says.
Consider the Swamp White Oak tree you walk past on a Philadelphia sidewalk. While the species is native to the region, the specimen likely started its life in a landscape far away, probably in Oregon’s Willamette Valley, and was transported in a refrigerated truck to a nearby nursery before being purchased and planted in the ground.
“If it’s a Philadelphia street tree, it could have travelled up to 4,400 miles before it arrives at the tree pit,” says Leah Kahler, a landscape designer and fellow at the McHarg Center for Urbanism and Ecology for the 2024-2025 Academic Year. “These trees might be native, but they are not local.”
The origins of your neighborhood’s tree canopy is just the kind of question that occupies Kahler, who worked as a landscape designer with Reed Hilderbrand before signing on as the McHarg Fellow. Some of her favorite days on the job were spent visiting nurseries, selecting trees for use in the parks and gardens she and her teammates designed. Often, a species that the designers at the Cambridge, Massachusetts, firm wanted for a particular project—a climate-adaptive or otherwise atypical plant, say—wouldn’t be available. It got Kahler thinking about the provenance of plants, their cultural associations, the environmental and climatic implications of the plant-product supply chain, and the meaning of so-called “native” plants.
Kahler, who started life in Baton Rouge, began teaching in Boston while working as a landscape designer. She was increasingly drawn to education, with an urge to “help equip entry-level designers with the conceptual and technical skills to push the field toward environmental justice goals.” As the 2024-2025 McHarg Fellow, her research and teaching focused on the movement of plants across cultures and the relationships between recreational and productive landscapes.
For an assignment to investigate terms related to landscape architectural practice, Master of Landscape Architecture student Andie Kennedy illustrated the evolution of horticulture from simple observation to intensive genetic manipulation.
This spring, Kahler taught a seminar titled Clones, Zones, & Migrants: Taking Stock of the American Plant Nursery Trade. The course was an investigation of plant movement, motivated by three questions: “Where do plants in designed landscapes actually come from? What does ‘native planting’ even mean for plants and political boundaries on the move? How might alternative methods of plant procurement change the way we design?”
Through a series of readings, lectures, and exercises, students explored the geopolitical underpinnings of contemporary horticulture and the cultural meaning of plants as a medium for design. In one exercise, students investigated specific terms related to landscape architectural practice, from “grafting” to “wild harvest” and “hybridization.” In another, they drew planetary-scaled “cartographic drawings” illustrating how plants move between different geographies.
Nitya Patel, a second-year Master of Landscape Architecture student, chose marigolds as her subject. The flowers are “used extensively in India for every happy or sad event,” Patel says. “They’re found everywhere.” But marigolds didn’t arrive in India until the 16th century, when Portuguese colonists brought them from Mexico. Eventually they supplanted a different flower in cultural rituals. Patel’s project explored “how a marigold would see the world.”
“It made me think about memory and how history is being written—how, culturally, things change,” Patel says. “Even though we think that this is how it has been forever, these movements of plants and culture have happened all throughout history.”
Kahler was drawn to teaching “to help equip entry-level designers with the conceptual and technical skills to push the field toward environmental justice goals.”
For a final exercise, Kahler asked students to work on a plot of land known as Highline Park, a remnant of Penn Park near the corner of 31st and Chestnut streets, below the Walnut Street Bridge. The assignment urged students to think through the concept of “reciprocal landscapes,” the relationships between designed spaces and the places where plant materials originate or end up. Holly Smithberger, a third-year Master of Architecture student, designed a network of “conversation pits” for the site, sunken areas for seating surrounding plots for plant propagation. The plants grown in the pits were meant to be used in vacant lots in Northeast Philadelphia by the Philadelphia Orchard Project. Smithberger selected the course as a way to learn more about plants after years of training in architecture.
“What I wanted to emphasize was the site being a bridge between Penn and the rest of Philadelphia, while also taking on this idea of care as labor and maintenance,” Smithberger says.
Kahler spent much of the last year interviewing nursery workers about their own practices and about their relationships with designers: their sourcing of seeds and propagation methods, shifting market demands, how they respond to changes in the climate. This fall, she will bring the research on the regional implications of faraway cultivation practices home to the Gulf Coast via a visiting research assistant professorship at Tulane University’s School of Architecture and the Built Environment and continue interrogating the environmental and cultural impacts of landscape architecture’s material practices.
“There’s an exciting, growing interest in the social and ecological implications of materials used in the construction of built landscapes, as well as in the labor conditions of the people who are foundational to making these landscapes. But so far, the far away geographies of plant production have not been studied as part of this political ecology of landscape architecture. I’m interested in what these landscapes of labor and production can tell us about how cultivation practices might align with—or fall short of—our field’s aspirations to environmental justice.
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