The Challenge: Growing Trees in a Complex Urban Landscape

Downtown Edmonton presents significant challenges for urban greening. The hard-packed soils typical of urban environments severely limit root development, leading to stunted tree growth and premature failure. Trees planted in such conditions often become infrastructure liabilities rather than assets, damaging pavements and requiring frequent replacements.

Additionally, existing infrastructure, including roadways, sidewalks, and underground utilities, limits the available space for tree roots to grow. Without a solution that could create healthy, uncompacted soil volumes below the pavement, the vision for a connected canopy would remain out of reach.

The Solution: Stratavault Engineered Soil Vaults

The transformation would be delivered in two phases. Phase one, completed between 2015 and 2016, extending from 111th Street to 116th Street (the focus of this case study). With funding cycles and project performance taken into account, phase two began in 2021 and carried through to 2023, continuing the same design approach from 116th to 109th Street.

To overcome these challenges, the City of Edmonton turned to Citygreen’s Stratavault system, a modular soil vault solution designed to support large volumes of healthy, uncompacted soil beneath pavements. These engineered cells build a matrix that caters for strong root development while simultaneously protecting surrounding infrastructure.

Installed under sidewalks and adjacent to tree planting areas, Stratavault enables trees to access the nutrients, air, and water they need for optimal growth.

Crucially, the system is designed to be structurally load-bearing, able to support surface infrastructure like pavements and street furniture without compromising root space.

In the case of 105th Avenue, the Stratavault system allowed soil volumes and root growth zones to be extended under walkways and hard surfaces, significantly increasing the rooting space available to each tree and giving them the best possible chance at long-term success.

Edmonton’s climate features significant seasonal variations, with dry summers and long, cold winters, making efficient water use and stormwater control key considerations for the project. The solution included permeable paving and large pipe

sweeps to be integrated into the Stratavault matrix. The design would restore natural systems in the urban environment, ensuring stormwater run off would be directed into the tree pits, being filtered by the roots and passively irrigating the trees.

This reduces the need for maintenance and supplemental irrigation, and helps manage runoff during heavy rainfall events, preventing water from overwhelming city drainage systems.

Since installation, the newly planted trees have flourished - growing rapidly and delivering the projected ten year canopy in just four years.The selected tree species have adapted well to the conditions provided by the Stratavault system, demonstrating vigorous health, strong root development, and early canopy closure.

This rapid growth has also brought cooling benefits to the corridor. By shading pavement and softening reflective surfaces, the new trees have helped reduce localized urban heat, making the street significantly more comfortable for pedestrians and cyclists during hot summer months.

The change along the avenue has been dramatic. Where there was once a gray, concrete-heavy environment, there is now a shaded, green, and welcoming streetscape. The project has enhanced not only visual appeal but also walkability and community use of the corridor.

In addition to environmental benefits, the newly established canopy supports biodiversity by attracting birds and pollinators, adding to the ecological richness of Edmonton’s urban core.

City officials and residents alike have expressed strong support and satisfaction with the transformation. The success of the project has demonstrated that high performance green infrastructure can be integrated into even the most constrained urban settings when guided by science, thoughtful design, and the right technology.

Outcomes and Lessons for Future Urban Greening

Citygreen worked closely with the City of Edmonton throughout the planning and implementation process, providing technical support, product expertise, and tailored design recommendations to meet the city’s specific needs. By leveraging Citygreen’s experience and solutions, Edmonton was able to create an urban canopy that is both functional and beautiful - setting a new benchmark for downtown streetscapes across Canada.

Key takeaways include:

• Soil Volume Matters: Healthy, uncompacted soil is the foundation of successful urban trees. Without it, trees struggle to survive, let alone thrive.

• Engineering for Resilience: Stratavault allows green infrastructure to coexist with a range of underground utilities and services.

• Fast ROI on Tree Investments: With proper soil conditions, trees grow faster and provide shading, cooling, and aesthetic returns much earlier than
expected.

• Community Value: Well-planned tree planting enhances walkability, comfort, biodiversity, and civic pride.