Opaque Ground: Reimagining Human-Soil Relations in the Lower Don
Award of Excellence
General Design
Toronto, Ontario, Canada
Rebecca Martin, Student ASLA;
Faculty Advisors:
Alissa North;
University of Toronto
Richly illustrated exploration of our essential but underappreciated soil and its role in renewing our urban environment. Thank you for the authentic graphics and personality that you have included within this submission.
- 2025 Awards Jury
Project Credits
Paula Davies
President, Todmorden Mills Wildflower Preserve
Janna Holmstedt
Artist, Researcher, & Gardener, Consulted on Urban Soils
Jenny Salmson
Urban Gardener, Soil Analyist, & Activist, Consulted on Urban Soils
Project Statement
Urban soil holds the residue of human activity while supporting visible and invisible non-human worlds. It is vital for regulating water cycles, storing carbon, and sustaining life, yet is often undervalued. In the face of biodiversity and climate crises, increased soil literacy is essential for designing resilient cities that work effectively with natural systems.
To promote soil literacy, this project proposes an urban soil survey and a series of experimental gardens along a 10-kilometer trail in Toronto’s Lower Don Valley Sub-watershed. These gardens integrate varying degrees of intervention with one rule: no new soil can be added. Instead, existing urban soil conditions are explored through collaborations with plant life.
Project Narrative
Urban soils reflect life in cities. Though often considered opaque, obscure, or degraded beyond value, they are complex systems that hold the residual impact of human activity over time. Using Toronto’s Lower Don River Sub-watershed as a case study, this project asks:
How can landscape architects work with urban soils as unique cultural landscapes whose character is made legible through plant life? How can we work with urban soil without dumping it as a waste material and replacing it with healthy soils extracted from elsewhere? How can we see, appreciate, and support the soil in our cities as it is, not as it might be without us?
To build and maintain healthy urban soils we must first build soil literacy. This project proposes an urban soil survey, and a series of experimental gardens designed to communicate soil survey findings along a 10-kilometer trail in Toronto’s Lower Don Valley Sub-watershed. Each garden begins with a simple rule: no new soil can be added. Instead, plants become intermediaries that convey below-ground conditions. These gardens are intended to be inter-species collaborations with varying degrees of human intervention, from full planting plans and ongoing maintenance schemes to gardens where successional processes are allowed to occur over time and only edges are maintained. In each garden, installation methods are low impact, prioritizing on-site materials and passive interventions.
Though sites would be selected after the survey is complete, five potential sites with different land-use and geologic histories have been identified to explore different garden strategies:
Site 1: Yonge and Eglinton – A dense mixed-use area and one of Toronto's Central Business Districts. On this site, ruderal species that can withstand harsh urban conditions will be planted in a manner that reframes their aesthetic interest.
Site 2: Todmorden Mills – A wildflower preserve on a former industrial site. On this site, a rammed earth wall will be placed to frame restoration work already underway by the Todmorden Mills Wildflower Preserve Stewardship Team.
Site 3: Don Riverbank – A river’s-edge clearing where invasive species are removed, but no new plants are introduced.
Site 4: Distillery District – A mixed-use heritage district near the downtown core. On this site, a circular clearing will be split by a sunken path: one half will be planted with ruderal species tolerant of dense urban environments, clay-heavy soil, and a high-water table; the other half will be left bare for natural succession to occur.
Site 5: Keating Channel Precinct – A former industrial area and car lot built on fill material. On this site, a 40m circle will be cleared for plants to arrive on their own. The edges will be maintained for legibility, but otherwise, successional processes will be allowed to occur uninterrupted.
All soil tells a story about the passage of time and the accumulation of processes. If we dispose of our “used” soils, then we lose valuable lessons about how our processes impact the ground and how the ground, in turn, impacts us. These gardens operate as living laboratories where the story of soil is told through plants. Over time, the gardens are designed to grow in complexity, offering adaptive, site-specific approaches to planting that foreground sensitivity to the soil as it is, not as it might be without us.
Plant List:
- Acalypha rhomboidea, Common Three-seeded Mercury
- Achillea millefolium, Yarrow
- Ageratina altissima, White Snakeroot
- Asclepias syriaca, Common Milkweed
- Caltha palustris, Marsh Marigold
- Cephalanthus occidentalis, Buttonbush
- Cichorium itybus, Chicory
- Cirsium discolor, Field Thistle
- Cornus sericea, Red Osier Dogwood
- Daucus carota, Queen Anne’s Lace
- Erigeron canadensis, Canadian Fleabane
- Geranium maculatum, Wild Geranium
- Helianthus annuus Common Sunflower
- Helianthus tuberosus, Jerusalem Artichoke
- Hydrophyllum virginianum, Virginia Waterleaf
- Hypericum kalmianum, Kalm’s St. John’s Wort
- Impatiens capensis, Common Jewelweed
- Lotus corniculatus, Bird's-foot Trefoil
- Matteuccia struthiopteris, Ostrich Fern
- Mirabilis nyctaginea, Wild Four o’Clock
- Monarda fistulosa, Wild Bergamot
- Oenothera biennis, Evening Primrose
- Podophyllum peltatum, Mayapple
- Rudbeckia hirta, Black-eyed Susan
- Sanguinaria canadensis Bloodroot
- Saponaria officinalis, Common Soapwort
- Schizachyrium scoparium, Little Bluestem
- Sedum acre, Biting Stonecrop
- Spiraea alba, White Meadowsweet
- Solidago canadensis, Canada Goldenrod
- Symplocarpus foetidus, Eastern Skunk Cabbage
- Ribes americanum, American Black Currant
- Rhus typhina, Staghorn Sumac
- Rumex crispus, Curled Dock
- Taraxacum officinale, Dandelion
- Trifolium repens, White Clover
- Typha latifolia, Broadleaf Cattail
- Vernonia missurica, Missouri Ironweed