Project Overview

The redevelopment of Morningside Avenue between Steeles Avenue and Passmore Avenue created an opportunity to build green infrastructure directly into a growing employment corridor. A new two-way multi-use path improved access for pedestrians, cyclists, and commuters, while 49 street trees were introduced to make the route greener and more comfortable over time.

Installed beneath the corridor in the summer of 2020, over 1,700 Silva Cells perform two important jobs. The system provides each tree with access to the soil needed for long-term growth while also creating an underground bioretention system that captures, distributes, and treats runoff from the surrounding roadway.

Take a visual tour of the project by watching the video above.

Multi-Use Green Corridor

The improvements were prompted by a major new development that brought hundreds of employees — and substantially more daily travel — to the area. Because many employees reach the site by public transit and complete part of their commute on foot, the corridor needed to function safely and comfortably for more than just vehicles. The new multi-use path established a dedicated connection for pedestrians and cyclists traveling between transit stops, workplaces, and the surrounding neighborhood.

The street trees and stormwater system give that transportation project an important green dimension. As the canopy develops, the trees will provide increasing shade and cooling along a route where people may otherwise be exposed to sun and heat. Below ground, runoff is managed within the same corridor. Rather than treating transportation, trees, and drainage as separate priorities, the project uses one coordinated landscape to support all three.

30 Cubic Meters of Soil Per Tree

Each of the 49 trees was designed with access to 30 cubic meters of soil, in accordance with the Toronto Green Standard requirements. That requirement is central to the story. It reflects an understanding at the policy level that planting a tree is not enough: cities must also reserve the belowground space trees need to establish, grow, and eventually develop substantial canopies.

To deliver that soil volume within a constrained streetscape, 1,702 Silva Cells — a combination of 1x and 3x configurations — were installed beneath the corridor. The system creates protected, uncompacted growing space below the hardscape while structurally supporting the surfaces above. Different system depths and stepped transitions allowed the design to respond to changing site conditions without sacrificing the overall soil-volume target.

Thirty cubic meters per tree represents a meaningful investment in the future urban forest. It gives roots room to expand beyond an isolated tree opening and creates the conditions for robust long-term growth. When soil volume is protected through municipal policy like the Toronto Green Standard (and then carried through design and construction) cities give their street trees a much better chance of becoming the large, high-performing canopy they envisioned.

Dual Function: Underground Bioretention

The soil beneath Morningside Avenue is also part of the project’s stormwater infrastructure. Runoff from designated catchment areas enters curbside catch basins positioned along the corridor. Before entering the Silva Cell system, the water passes through a CB Shield that provides first-flush pretreatment by intercepting debris and pollutants.

From the catch basins, non-perforated inlet pipes convey the runoff to 150-millimeter perforated distribution pipes installed in the Silva Cell soil profile. These distribution pipes are laid level, allowing water to spread across the soil zone rather than concentrating at a single tree opening. As the runoff moves through the planting soil, it can be filtered, temporarily stored, and made available to the trees as passive irrigation.

At the base of the system, perforated underdrains collect treated excess water and carry it toward the storm sewer. This sequence — capture, pretreatment, distribution, soil filtration, and controlled drainage — helps improve water quality and reduce the rate at which runoff reaches the conventional drainage system. The same uncompacted soil that supports the trees therefore becomes functional stormwater infrastructure beneath the multi-use path.

Canopy Taking Shape

In only a few growing seasons, the beginnings of the future canopy are becoming visible. That canopy will be particularly valuable along a route designed for people walking, cycling, and traveling to and from public transportation. As the trees continue to grow, they can provide more shade, reduce exposure to summer heat, intercept additional rainfall, and make the corridor feel increasingly welcoming.