Providing Best Soil Volumes for Healthy Trees with Stratacell

By Nadia Geagea Pupa

With the largest collection of Victorian-era industrial architecture in North America, the Distillery District in Toronto, Ontario, Canada is a true historic and entertainment destination located east of the downtown. This is also known as Canada’s largest pedestrian-only precinct for arts, culture, and entertainment. In fact, it is such a high-profile destination, that the Prince of Wales and the Duchess of Cornwall, made a visit to the area in May of 2012 during their tour of Canada.

The Distillery District is characterized by its traditional brick-paved streets and lanes, which are catered for pedestrians and cyclists. Regular motor traffic is restricted to streets and parking areas, which are located outside of the district’s historic center. There are also many public spaces where pedestrians can relax and socialize; these areas are specifically designed to encourage visitors to spend time in its spaces. Specific to these areas are the trees and the importance they bring to the streetscape. In order for these public spaces to maintain their ease of access and beautiful appearance, it is vital to ensure that the trees remain healthy.

The recent renovation project that took place in this district required a group of visionaries which included landscape architects and urban planners and designers who had great plans for this space to create an attractive pedestrian environment.

“This is a very special place in Canada with the largest collection of heritage-style architecture, but at one point in time, it was a very isolated place before major changes were made,” said David Mugford, BLA, ASLA, of The Planning Partnership—a multidisciplinary practice providing land use planning, urban design, landscape architecture, and consultation services to public and private sector clients.

The Planning Partnership was heavily involved in the renovation project, especially when the major scope of the project shifted its focus to creating stabilized slopes to the streetscape and planting on brick-lined pedestrian walkways.

“Throughout the planning process, we conducted extensive soil and water tests to ensure that the trees being planted would have enough oxygen to survive and grow,” said Michael Ormston-Holloway, BSc, MScP, GDHort, MLA, Associate of Planning Partnership and ISA Certified Arborist. “We really wanted to look at what failed in the past, such as high water tables and issues with oxygen, which caused soil compaction and standing water that were not good for tree growth.”

Issues of soil compaction were a major concern especially for the three tree pits and 15 trees that were planted at the Distillery District, which is why Ormston-Holloway and Mugford explained the reasoning behind using the Stratacell™ system for this project.

“We wanted to do a good job of armoring the soil to prevent issues of soil compaction that can happen over time, especially near vehicular routes,” said Ormston-Holloway. “It’s always a big goal to maximize the soil volume for tree root growth, and that’s exactly why we chose to work with the Stratacell system. It provided a tree vault with more strength, which the trees needed for survival compared to other products out there.”

The Stratacell system provided the strength to protect the trees and soil cells to withstand motor or pedestrian activity on the surface, especially since the trees were planted in close proximity to vehicular routes. Throughout the project planning, there were also concerns among clients to meet H20 Loading and AASHTO standards, which further addressed why the strength provided by the Stratacell system made this a beneficial choice for being used.

According to John Badali of Islington Nurseries, about 800 units of the Stratacell system were used. “It’s a really quick snap together system, you don’t have to compact the soil inside it,” he said. “We simply loaded the soil into the matrix to allow the roots room to grow.”

As an installation best practice, Badali explained the importance of excavating the area and leveling the base before placing the Stratacells in the ground. “The Stratacells are color coded for their strength,” he explained. “There’s a little diamond symbol that represents the strength that they’re able to withstand. We were able to link them together both horizontally and vertically to ensure solid support for the trees.”

“Citygreen® provided us with engineered drawings to assure the designers and clients that the Stratacell would meet these H20 load requirements,” said Ormston-Holloway. “This was a great benefit, and helped to assure the clients.”

“Another benefit of using the Stratacell came into play when we had to deal with the paving and deep underground garage parking,” added Mugford. “Dealing with this limited profile gave us a fine-grain approach to layer the Stratacells to allow us to get the maximum soil volume possible, especially since these trees can go into constrained conditions pretty easily.”

In the past, it was noted that the Japanese Zelkova trees that were previously planted in the area slowly died over a period of a few years due to the lack of suitable soil. Therefore, a wide variety of different tree types were chosen based on the ability to withstand the potential for soil compaction and also extended periods of time in standing water—especially since the Distillery District is located in close proximity to the Toronto Waterfront.

The different tree types that were planted include swamp white oaks, black gum (or tupelo), weeping golden willow, trembling aspen, Morton glossy elm, yellow poplar, and European larch. The variety of these trees contributes to the beautiful, updated streetscape of the Historic Distillery District. As urban planners and landscape architects continue to make changes to upgrade the Toronto area, they are mindful to provide places for healthy trees to grow based on the current conditions, and make the best choices for trees to thrive.

“The knowledge that Citygreen offered gave us the ecological ammunition behind the decisions we made,” said Mugford. “It’s a well-researched company that has done their homework, which also makes it easier for someone to use their product.”

“There are many products that come out that require a lot of training,” said Badali. “But we don’t have the time to spend on training. The day of installation for the Stratacells, a CityGreen rep came out and gave us a demo; they are just really friendly people to work with. They were very helpful.”