Is Green Infrastructure Expensive?

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Green Infrastructure is seen as expensive when compared to traditional grey infrastructure.

But with the increase of green infrastructure technology is this actually the case?

A study comparing the actual project costs to typical costs for conventional development found that 11 out of 12 diverse projects with direct cost comparisons between conventional and green infrastructure approaches showed cost decreases averaging 36%.

Green infrastructure, such as soil vaults and permeable pavement, can lower water treatment costs, reduce flooding, and erosion, thus providing economic and environmental benefits to the city.

What are the Typical Costs of Green Infrastructure Projects?

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The cost of green infrastructure can be influenced by factors such as the type of project, location, and integration with planned infrastructure improvements.

Integrating green projects with planned infrastructure improvements, such as road reconstruction or roof replacements, can lead to cost savings of 30% to 60% over the lifetime of the project due to the multiple benefits that green infrastructure offers back to the built environment. 

It is important to note that the cost of green infrastructure is not solely determined by the initial construction costs but also includes life cycle costs, including planning, design, installation, operation and maintenance, and replacement. 

The cost-analysis of green infrastructure should be analyzed in conjunction with its performance and the multiple benefits it provides, including environmental, economic, and community benefits.

How do Cities Fund Green Infrastructure Projects?

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Cities typically fund green infrastructure projects through a variety of mechanisms, including public and private sources. Some of the common funding sources and mechanisms highlighted in the search results include:

  1. Public Sector Financing: Cities can use their main revenue sources, such as property taxes, transport fees, and other charges, to finance green infrastructure projects. They can also explore the greening of municipal financial instruments, such as congestion charges, variable parking fees, toll lanes, and split-rate property taxes, to achieve greener urban infrastructure1.
  2. Private Sector Involvement: Public-private partnerships (PPPs) are a common mechanism for involving the private sector in funding green infrastructure projects. In PPPs, the long-term risk is transferred to the public sector, and they can play a significant role in financing and implementing green infrastructure projects1.
  3. Grant Funding: Grant funding, including federal grants, can provide local governments with the resources to implement green infrastructure projects. However, federal grants can be highly competitive2.
  4. Federal Programs: Federal programs that support efforts to reduce water pollution and manage stormwater can provide funding for green infrastructure projects. For example, the Environmental Protection Agency (EPA) provides funding for such projects.
  5. Community Development Funds: Community development money can be used to fund green infrastructure projects because these projects can create jobs, increase economic activity, and increase property values. Urban tree planting and green infrastructure can increase economic activity in a commercial district and property values by mitigating flooding and improving neighborhood aesthetics3.
  6. Transportation Funding: Green infrastructure projects are often eligible for transportation funding because they improve transportation networks by efficiently and cost-effectively mitigating street and alley flooding and create a cooler more comfortable environment for passengers.

A great way to ensure green infrastructure gets built is to set it as a building standard for new constructions and incorporate GI into street layouts and designs.

Citygreen regularly works with local and state governments worldwide to improve their city standards towards tree canopy and green infrastructure. Our team can advise you on actionable goals and solutions to cool your city with green solutions.

How To Do Green Infrastructure Cost Analysis?

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To conduct a green infrastructure cost analysis, the following steps can be taken:

  1. Define Green Infrastructure and Public Space: Green infrastructure is the network of green spaces, natural systems, and semi-natural systems that support sustainable communities, while public spaces are places publicly owned or for public use, accessible and enjoyable by all free and without a profit motive.
  2. Cost Benefit Analysis: Measure incremental change relative to what would have happened without action, i.e., the base case. The CBA should only consider the incremental or marginal impact of a program or project. Specify the base case in as much detail as possible and quantify it to set a baseline for the incremental changes in outcomes that are being measured. including identifying the developing options, identifying and forecasting costs and benefits, valuing costs and benefits, identifying non-market impacts, and reporting the results of CBA.
  3. Consider the Costs of Green Infrastructure and Public Space: The costs of such projects include construction costs, costs related to the replacement of capital, and costs related to ongoing maintenance and operation. Cost estimates should be specific to the individual project and reflect the design and conditions associated with the construction and operation of the project.
  4. Value the Benefits of Green Infrastructure and Public Space: The benefits of public space are driven by a range of features, and the framework provides recommended approaches and parameters for valuing these benefits. It’s important to carefully consider the specific benefits associated with the project and apply the recommended parameters accordingly.
  5. Engage with Stakeholders: In addition to using the framework, practitioners should engage with stakeholders, including the department’s subject matter experts and the community to understand the full use case of the infrastructure.

By following these steps, practitioners can conduct a comprehensive green infrastructure cost analysis that takes into account the economic, social, environmental, and cultural costs and benefits of the project.

What are the Benefits of Green Infrastructure?

green infrastructure being used to cool a outdoor shopping centre in australia

There are a multitude of benefits related to green infrastructure that cities that consistently invest in green infrastructure are seeing.

Energy Efficiency

Green Infrastructure reduces the cooling demands of households, and buildings through creating shade and transpiration of water through leaves from trees and plants. The NSW government estimates that for each reduction in degree through tree canopy you decrease your energy bill by $13.

Air Quality Improvement

Increasing tree canopy and urban green walls contribute to air quality improvement through capturing of physical and gaseous pollutants, suspending captured particles, emitting environmentally friendly particles like pollen, and disrupting of wind flows through tree canopy.

Water Management

Green Infrastructure can capture water runoff, which reduces the volume of stormwater that needs to be processed and be used to sustain the green infrastructure itself. It additionally improves the water quality of runoff that does reach the waterways.

In the ‘Valuing green infrastructure and public spaces Framework’ from the NSW Government. The estimate the value of stormwater reduction based on the avoided costs of projects to build additional stormwater management infrastructure like wetlands and retention ponds.

Some key data points from that analysis:

  • Cost to manage stormwater flows ranged between $0.04 to $0.30 per cubic metre captured, depending on the type of infrastructure option
  • An average-sized street tree in Canberra captures 16,500 L (16.5 cubic metres) annually
  • A hectare of irrigated urban forest would capture 1 megalitre (1,000 cubic metres) of stormwater per 20 mm rain event

So in summary, the document states green infrastructure and trees can reduce stormwater runoff, avoiding the need for additional “grey” stormwater infrastructure. This avoided expenditure provided an approach to quantifying the stormwater management benefits.

Health Benefits

Green Infrastructure has far ranging impacts in the areas of mental and physical health. Increasing the amount of green infrastructure in the forms of public open spaces, parks, and facilities shows a 6% increase of residence hitting their daily activity goal which equals around a $1.13 cost saving per household per km walked.

Urban cooling through tree canopy and transpiration also reduces heat-related health complications. The NSW Government estimates 1°C of cooling saves $3 per person per very hot day in health costs and an 10% increase in canopy cover is equal to a 1.1°C cooling effect.

We invited General Practitioner Dr. Kim Loo to come speak at our event ‘Where Shade hits the Pavement’ to discuss how trees and urban planning are impacting her patients in Western Sydney.


Despite its complexity, the wide-ranging benefits of green infrastructure unfold gradually over time. While there exists an initial upfront cost during the construction phase, this investment quickly shows substantial returns, growth and impact for the community.

As the effects begin to manifest in the economic, social, and environmental spheres, the return on investment becomes increasingly evident. The transformative power of green infrastructure becomes apparent when measuring its positive influence on economic savings, social well-being, and environmental sustainability.

Therefore, while the initial costs might seem substantial, the long-term advantages and dividends gained from the implementation of green infrastructure undoubtedly outweigh these initial expenses, making it a wise and forward-thinking investment for communities and regions alike.

How to Build Resilient Cities with Green Infrastructure

Green Infrastructure used to cool and beautify a main street in Canada

What is Green Infrastructure?

Green infrastructure refers to urban infrastructure of natural or semi-natural systems strategically designed and implemented to manage water, air quality, biodiversity, and other environmental issues in cities and urban environments. It utilizes natural processes and vegetation to provide diverse ecosystem services, contributing to the overall sustainability and resilience of communities.

Key components of green infrastructure include:

  1. Natural Vegetation: This includes parks, forests, wetlands, green roofs, street trees, and other forms of vegetation that help absorb rainwater, mitigate urban heat, improve air quality, and provide habitats for wildlife.
  2. Water Management Systems: Green infrastructure incorporates features like rain gardens, bioswales, permeable pavements, and retention ponds to manage stormwater, reduce flooding, and enhance groundwater recharge by allowing water to infiltrate the soil rather than running off into sewers.
  3. Urban Design: It involves integrating green spaces and natural elements into urban planning and development, encouraging mixed-use spaces, promoting walkability, and creating connections between green areas to enhance the overall urban environment.
  4. Ecosystem Services: Green infrastructure aims to provide a range of services, including improved air and water quality, biodiversity support, climate regulation, carbon sequestration, and enhanced aesthetic and recreational values for communities.

The primary goal of green infrastructure is to mimic and restore natural processes, promoting environmental sustainability while simultaneously offering economic and social benefits to communities. By integrating natural elements into the built environment, green infrastructure helps address environmental challenges, adapt to climate change impacts, and create healthier and more resilient living spaces.

Why are Resilient Cities Important?

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Resilient cities are crucial for adapting to ongoing challenges such as climate change, minimizing risks, ensuring socio-economic stability, promoting environmental sustainability, prioritizing public health, and fostering long-term prosperity. Building resilience is an essential step towards creating safer, more sustainable, and thriving urban environments.

Table of Contents

Is Green Infrastructure Important for Urban Planning?

In a nutshell, Yes. Green infrastructure and public spaces play an crucial role in cooling and improving the quality of life and community wellbeing.

  • Green infrastructure benefits urban areas by improving air and water quality, reducing the urban heat island effect, enhancing biodiversity, and promoting health.
  • Various types of green infrastructure include green roofs, living walls, rain gardens, permeable pavements, urban forests, soil cells, stormwater tree pits, and green spaces.

Defining Green Infrastructure and Its Role in Urban Planning

Green infrastructure, a key concept in urban planning, involves integrating natural elements and processes into urban development. Green Infrastructure aims to reintroduce the environmental lifecycle back into cities and urban environments to improve environmental quality, promote sustainability, and improve the overall well-being of urban communities. Green infrastructure will continue to grow and become a pivotal consideration in local governments and cities are they plan to create liveable, resilient cities by addressing environmental challenges and fostering sustainable growth.

It encompasses a wide range of practices, methodologies, and technologies that are crucial for ensuring the long-term sustainability of cities. Green infrastructure offers a holistic approach to managing urban spaces, taking into account the interconnectedness of natural systems and human activities.

Rapid urbanization has led to significant environmental and social challenges, including air and water pollution, loss of green spaces, and heightened exposure to extreme weather events. Green infrastructure provides a means to counteract these impacts by promoting ecological balance, conserving natural resources, and creating more resilient and livable urban environments.

Benefits of Green Infrastructure in Urban Planning

Improving Air and Water Quality

Green infrastructure improves air and water quality within urban areas. Green spaces act as natural filters, capturing pollutants and mitigating the effects of air pollution. Additionally, green infrastructure features, such as bioswales and rain gardens, help manage stormwater and enhance water quality.

Reducing Urban Heat Island Effect

Urban heat islands pose significant challenges for urban residents. Green infrastructure, including green roofs and tree canopies, helps mitigate the urban heat island effect by providing shade, reducing surface temperatures, and promoting evaporative cooling, creating more comfortable and thermally balanced urban environments.

Enhancing Biodiversity and Ecosystem Services

By integrating green infrastructure, cities can support biodiversity and enhance ecosystem services. Urban green spaces and corridors provide habitats for diverse plant and animal species, contributing to the preservation of local biodiversity. Furthermore, green infrastructure promotes ecosystem services such as pollination, carbon sequestration, and natural pest control.

Mitigating Climate Change Effects

Green infrastructure plays a vital role in mitigating the impacts of climate change within urban areas. By increasing vegetation cover and promoting sustainable water management, green infrastructure helps reduce greenhouse gas emissions, combat urban heat, and enhance the overall resilience of cities in the face of changing climatic conditions.

Promoting Health and Well-being for Urban Residents

The presence of green infrastructure in urban settings has been linked to numerous health benefits for urban residents. Access to green spaces and natural environments has been associated with reduced stress, improved mental well-being, increased physical activity, and overall enhanced quality of life.

Benefits of Green InfrastructureTypes of Green Infrastructure
Improving Air and Water QualityGreen Roofs
Reducing Urban Heat Island EffectRain Gardens and Bioswales
Enhancing Biodiversity and Ecosystem ServicesPermeable Pavements and Green Streets
Mitigating Climate Change EffectsUrban Forests and Tree Canopies
Promoting Health and Well-being for Urban ResidentsGreen Spaces and Parks
Increases the property value of through treesBlue-Green Infrastructure for Stormwater Management
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Types of Green Infrastructure that help Cities the Most


Adding trees to urban spaces, plazas, streets, city blocks, downtown CBDs, is probably the most effective way to cool urban spaces and increase the liveability of our cities.

Trees provide immense benefits to a community, far beyond just aesthetic value. They offer immediate shade to protect against the heat of the sun. Through transpiration from their leaves, they cool surrounding areas. Their root systems and leaves absorb particular matter and pollutants from both air and soil. Trees improve physical and mental health by encouraging outdoor recreation in their cool shade. Increased green canopy has even been shown to sharpen mental cognition.

Additionally, trees support biodiversity by sustaining natural ecosystems. In all these ways, planting the right trees can greatly enhance urban spaces.

Related: Why we need Trees in our Cities?

Green Roofs

Green roofs can offer similar benefits to trees but add value as they can be planted on roofs to help dissipate the urban heat island effect as a major factor in creating the heat island is the reflection of heat from hardscapes such as cement, roads, and rooftops back into the atmosphere. The installation of vegetation on rooftops, provide benefits such as improved insulation, stormwater management, heat island mitigation, and the creation of urban wildlife habitats.

Rain Gardens and Bioswales

Rain gardens and bioswales are designed to capture and absorb stormwater, preventing runoff and reducing the burden on traditional drainage systems, thereby improving water quality. A new innovation in this space is connecting the stormwater system into the soil cells that hold trees. This gives the trees access to on-site water reducing the need for external irrigation, improves the quality of the water as the tree through its tree roots and soil clean the water of pollutants. Excess water now cleaned by the tree can be stored in a pit under the tree and released back into the cities sewerage system at a later date reducing the impacts of high level rain events and flash flooding.

Permeable Pavements and Green Streets

Permeable pavements and green streets allow water to infiltrate the ground, reducing surface runoff and contributing to groundwater recharge while minimizing flooding risks.

Urban Forests and Tree Canopies

urban forest planted to grow a large tree canopy to shade the new apartment buildings

Urban forests and tree canopies play a crucial role in mitigating air pollution, providing shade, and enhancing the aesthetic appeal of urban landscapes.

Environmental Benefits:

  • Trees help reduce the urban heat island effect by providing shade and cooling through evapotranspiration. This allows urban planners to plan for less electricity usage for cooling.
  • Trees absorb air pollution, store carbon, and filter particulates which improves air quality. This enables healthier urban population densities.
  • Tree canopies slow and reduce stormwater runoff, reducing strain on drainage systems. This allows smarter water management systems.
  • Trees provide wildlife habitat, enabling the incorporation of biodiversity in urban planning.

Economic Benefits:

  • Studies show property values increase with more surrounding trees and greenery. This provides higher property tax bases.
  • Trees provide natural noise reduction capabilities, enabling closer proximities between certain land uses.
  • Tree-lined retail areas have shown increased sales and attraction of businesses. This spurs economic revitalization.

Social Benefits:

  • Access to trees and green space provides mental/physical community health benefits. This allows for planning recreational spaces.
  • Trees provide natural privacy separation between incompatible land uses.
  • Urban forests aid in placemaking and establishing community identify and pride.

What is Blue-Green Infrastructure for Stormwater Management?

Blue-green infrastructure integrates natural and engineered water systems to manage stormwater, reducing flood risks and enhancing water quality in urban areas.

Stormwater pipes integrated into a stratavault soil cell to help reduce flooding and water the tree
Caption: Stormwater pipes integrated into a Stratavault soil cell to help reduce flooding and water the tree

The stormwater management potential of blue-green infrastructure in reorganizing our cities to be more resilient is a powerful concept as we can harness the power of natural processes to capture and filter rainwater right where it falls. Just imagine—rain gardens, green roofs, and bioswales of lush native vegetation growing our city, beautifying neighborhoods while putting stormwater to work!

This approach relies on the water-cleaning talents already found in soils and plants. It’s a decentralized network that keeps working even when one part fails. And it can adapt to handle bigger storms coming our way with climate change as Trees can absorb between 10 and 150 gallons of water daily.

Beyond stormwater perks like less flooding and pollution, blue-green infrastructure also provides habitat, cleaner air, urban heat relief—really boosting quality of life for all inhabitants across our communities.

Implementing it takes some upfront planning to get plant and soil selections right. But once established, the nature-centric approach lets vegetation and microbiology do the water treatment work for us! Plus, the infrastructure cost savings are substantial when you consider the pipe and treatment plant alternatives over the lifetime value of the project because as the trees and green spaces continue to grow the benefits just compound.

At Citygreen we’re convinced blue-green infrastructure is the sustainable, resilient way forward for both stormwater and the livability of our public spaces.”

If you’re interested in partnering with us to help create sustainable stormwater management solutions for your project. Use our Contact form below and one of our Urban Greening Consultants will be in touch.

Case Studies

Successful Implementation of Green Infrastructure in a Car Park

Several cities have successfully implemented green infrastructure projects, such as New York City’s High Line and Singapore’s Gardens by the Bay, demonstrating the transformative potential of green infrastructure in urban environments.

Positive Impacts and Transformations Resulting from Green Infrastructure Integration

The integration of green infrastructure improves urban resilience, enhanced environmental quality, and the revitalization of communities, fostering a new era of sustainable urban development. Watch our above case study on how a new sporting development in Edmonton, Canada used soil cells and trees to capture stormwater to support the cooling of parked trees and reduce the strain on the cities municipality system.

Challenges and Barriers of Green Infrastructure for Urban Planning

Education and Community Engagement

The lack of public awareness and education poses a barrier to implementing more green infrastructure as a lot of greenery is seen as a purely aesthetic value and the majority of stormwater infrastructure lives underground away from prying eyes so aware is lower compared to other strategies.:

  1. There may be misconceptions about effectiveness. Without seeing successful examples or understanding the water management capabilities of natural systems, the public may doubt whether green infrastructure can handle stormwater at the necessary scale or provide sufficient flood protection. Communicating proven results is key.
  2. Aesthetic concerns may arise. Bioswales, rain gardens, and other green systems look much different than conventional pipes and concrete channels. Some residents may perceive the vegetation and soil to be unkept or not properly “engineered”. Showcasing attractive, well-maintained projects can overcome this bias.
  3. There tends to be familiarity with the status quo gray infrastructure, but less knowledge of decentralizing systems that distribute absorption and infiltration capacities across neighborhoods. Explaining the logic and localized benefits (like cooler parks) facilitates acceptance.
  4. Funding proposals for novel approaches face skepticism if people don’t grasp the multiple functions provided, from stormwater management to community wellness perks. Quantifying budget savings vs gray infrastructure, recreational use values, air quality indexes, etc. builds a stronger case.

Limited Space and Land Use Conflicts

The limited availability of space and conflicts with existing land uses present challenges for the integration of green infrastructure, requiring innovative solutions to optimize spatial utilization. This is a key reason soil cells like stratavault and stratacell can be so beneficial in a project due to the value add of managing stormwater while supporting the tree roots.

Economic Costs and Financial Incentives

The upfront costs associated with green infrastructure implementation can pose financial challenges for cities, developers, and specifiers, as there are many stakeholders in large scale projects, so emphasizing the need for financial incentives and innovative funding mechanisms to support sustainable urban development. But the legacy of a green space or tree that will continue to support it’s community for the next 50 years is a key investment worth fighting for.

Regulatory and Institutional Obstacles

Lack of Regulatory practices and institutional complexities may impede the seamless integration of green infrastructure, necessitating green policies and the streamlining of administrative processes will help increases the green liveability of your local community and cities helping to reach climate targets sooner.

Addressing Equity and Social Justice Concerns

Equity considerations are critical in ensuring that green infrastructure benefits are equitably distributed across diverse communities, necessitating inclusive and equitable planning approaches. Lower socio-economic areas generally have less green canopy which exacerbates issues such as urban heat, cooling, and medical health problems.

Policy and Planning Considerations

Government Policies and Regulatory Frameworks

Government policies and regulatory frameworks play a pivotal role in facilitating the integration of green infrastructure, requiring supportive policies, incentives, and standards for sustainable urban development.

Integrated Urban Planning Approaches

Integrated urban planning approaches that prioritize green infrastructure can optimize land use, enhance environmental quality, and promote the efficient use of resources within urban areas.

Zoning and Land Use Planning for Green Infrastructure

Zoning and land use planning strategies can be leveraged to incentivize and mandate the incorporation of green infrastructure elements into urban development projects, ensuring the systematic integration of sustainable practices.

Community Engagement and Education

Importance of Community Participation in Green Infrastructure Projects

Community participation is essential for the success of green infrastructure projects, emphasizing the need for inclusive decision-making processes and the active involvement of local residents.

Public Awareness and Education Campaigns

Public awareness and education campaigns can foster a deeper understanding of the benefits of green infrastructure, mobilizing support and advocacy for sustainable urban development initiatives. Penrith City Council ran a deep public campaign to its community around the benefits of trees to help increase the uptake of free tree plantings in their front yard.

Collaborative Decision-making Processes

Collaborative decision-making processes involving stakeholders and local communities can lead to more informed and inclusive urban planning, ensuring that diverse perspectives are considered in green infrastructure projects.

Collaboration and Partnerships

Engaging Stakeholders and Local Communities

Engaging a diverse range of stakeholders, including residents, businesses, and community organizations, fosters collaborative partnerships and ensures that green infrastructure projects are aligned with local needs and priorities.

Public-Private Partnerships for Green Infrastructure Initiatives

Public-private partnerships offer opportunities for leveraging resources and expertise, facilitating the implementation of green infrastructure projects and promoting innovative financing models.

Multi-sectoral Collaboration and Networking

Multi-sectoral collaboration and networking enable the integration of diverse perspectives and expertise, fostering holistic and innovative approaches to green infrastructure planning and implementation. to further this goal we created the ‘Where the Shade hits the Pavement’ event to get the top professional in a range of industries to come speak to how we can improve the cooling and liveability of our cities.

See the full talks from the day here.

Smart Technologies and Data-driven Planning for Green Infrastructure

The integration of smart technologies and data-driven planning processes can optimize the design and management of green infrastructure, enhancing its effectiveness and adaptability in evolving urban environments.

Nature-based Solutions and Biophilic Urban Design

The adoption of nature-based solutions and biophilic urban design principles can further enhance the integration of green infrastructure, creating urban environments that prioritize nature, human well-being, and ecological resilience.

Innovative Financing Models for Sustainable Urban Development

Innovative financing models, such as green bonds and impact investing, offer opportunities to secure funding for green infrastructure initiatives, supporting the long-term sustainability of urban development projects.

Summary of Key Points and Key Takeaways

Green infrastructure will plays a pivotal role in shaping sustainable and resilient cities,

Emphasizing the Role of Green Infrastructure in Shaping Sustainable and Resilient Cities

The integration of green infrastructure is essential for addressing the challenges of urbanization, fostering environmental stewardship, and creating cities that are adaptive, sustainable, and inclusive.

Call to Action for Integrating Green Infrastructure into Future Urban Planning Initiatives

A call to action is issued for the integration of green infrastructure into future urban planning initiatives, emphasizing the imperative of prioritizing sustainable and resilient urban development.

Resources and Further Reading

For readers interested in delving deeper into the topic of green infrastructure and urban planning, the following resources are recommended for further exploration:

  • “Green Infrastructure: A Landscape Approach” by David C. Rouse
  • “Designing for Hope: Pathways to Regenerative Sustainability” by Dominique Hes and Chrisna du Plessis
  • The Nature Conservancy’s Urban Conservation web page
  • The U.S. Environmental Protection Agency’s Green Infrastructure website

For access to additional information and support related to green infrastructure and urban planning, the following organizations and online resources are valuable references:

  • The International Society of Arboriculture (ISA)
  • The American Society of Landscape Architects (ASLA)
  • The World Green Infrastructure Network (WGIN)
  • The United Nations Human Settlements Programme (UN-Habitat)

In conclusion, the integration of green infrastructure is essential for building resilient, sustainable, and livable cities. By addressing environmental challenges, promoting community well-being, and fostering innovation, green infrastructure offers a pathway to shaping the future of urban development in harmony with nature.

Answers To Common Questions

Who benefits from green infrastructure in urban planning?

Green infrastructure benefits both city residents and the environment by improving air and water quality.

What is the role of green infrastructure in urban planning?

Green infrastructure in urban planning involves integrating natural elements like parks and green roofs to manage stormwater and reduce heat islands.

How does green infrastructure impact urban planning?

Green infrastructure impacts urban planning by promoting sustainability, enhancing resilience, and creating healthier urban environments.

What are the challenges of implementing green infrastructure in urban planning?

One challenge is the initial cost, but long-term benefits such as reduced maintenance costs and improved public health can outweigh this.

How can cities overcome objections to green infrastructure in urban planning?

Cities can overcome objections by educating stakeholders about the long-term benefits and cost savings associated with green infrastructure.

Who is responsible for implementing green infrastructure in urban planning?

At a high level the asset owners are responsible for creating a cool liveable space. Urban planners, city officials, and community stakeholders all play a role in implementing green infrastructure in urban planning

How Much Soil Do Street Trees Need?

How much soil do street trees need? It's a question that frequently arises in the workshops we conduct around the world.

Striking the perfect balance is essential to provide street trees with the optimal conditions for their growth, including ample nutrients, sufficient space for root expansion, and effective water drainage. In order to fully comprehend the requirements of soil and the intricate interactions occurring underground, several crucial aspects deserve our attention.

A commonly used field reference for soil is: two cubic feet of loam soil for every one square-foot of tree canopy (at tree maturity). Simply stated, a mature tree that provides 400 square-foot of canopy should be planted with 800 square feet of quality soil. Studies demonstrate that the quality loam soil grows trees that have 300 times more leaves and are 1.7 times taller than those grown in compacted soils. (Magill & Leake, 2013)

Let's explore the key considerations when it comes to soil and the vital role it plays in supporting healthy and thriving street trees.

Root Zone Protection

Tree roots will explore looking for water, nutrients and space for growth. As long as there is adequate moisture, nutrients and oxygen they will extend far beyond the canopy area. Compaction and damage to the root zone can severely impact a tree's health and longevity. Implementing measures like root barriers, and tree grates can help preserve the critical root zone and promote the overall well-being of street trees.

Soil cells like Citygreen Stratavault are purposely designed to house high quality uncompacted soil and tree roots under urban environments like roads, and pavements. Soil cells offer the tree ideal underground growing conditions while ensuring the tree roots are contained to avoid impacting surrounding urban infrastructure.

Related: How Tree Roots Behave
workers installing a tree in a soil cells stratavault

Soil Composition

The composition of soil plays a crucial role in supporting tree growth. It should strike a balance between water-holding capacity and drainage. Soil should be well-draining to prevent waterlogging and root rot, yet retain enough moisture for trees to access during dry periods. The right mix of organic matter, minerals, and proper pH levels is essential for optimal tree health.

Existing Utilities

Careful planning and coordination is necessary to ensure that tree planting and root growth do not interfere with or damage existing underground services. Conducting thorough site assessments and consulting with utility providers can help identify potential conflicts and allow for the implementation of tree-friendly solutions.  Read about a recent tree retrofitting we did here.


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Soil Compaction

Soil Compaction hinders the tree's ability to establish a robust root system due to having to waste so much energy moving through the highly compacted soil, leading to stunted growth, nutrient deficiencies, and increased vulnerability to pests and diseases. Implementing strategies to alleviate soil compaction, such as aeration techniques and proper soil management practices, is crucial for maintaining healthy street trees and promoting their long-term vitality.



high quality soil being put in soil cells to provide the tree with adequate soil compact for optimal growth

How Citygreen tackles all these issues

Citygreen's comprehensive approach to urban tree planting and green infrastructure brings over 30 years of experience into providing effective solutions. Our range of soil cells, trees grates, stormwater management, tree guying, and tree protection solutions guarantees we have the solution to any urban tree problem.

Contact our team to discuss how we can help you plant more trees in your next Urban Project.


urban street tree installed in road

What is Structural Soil?

Structural soil is used in the world of urban landscaping, particularly for urban tree-planting projects. With its unique composition, structural soil plays a crucial role in providing a supportive environment for tree roots to thrive in challenging urban environments. 

Structural soil is a specially engineered soil mixture designed for two distinct purposes;

  1. Provide a solid structural foundation for the surrounding urban infrastructure.
  2. Give trees access to nutrient soil in tricky urban environments.

Structural soil is not your typical soil blend— It’s made up of 80% gap-graded materials (crushed stones, etc) and 20% soil. Structural soil is generally compacted under a pavement system like a road or footpath to give structural support, creating minimal void spaces to ensure strength for the above and surrounding infrastructure.

the difference in soil volume in structural soil vs a soil vault

Difference in soil volume between structural soil & a soil vault

As highlighted in the graphic above the 'void space' shows the space available for soil that trees can actually use. When comparing Structural soil to soil vault systems(soil cells) such as Stratavault we see the dramatic difference in available soil. This is one of the key reasons soil vault systems grow high-quality and larger trees in a shorter time.

Is Compacted Soil Good for Tree Growth?

No, Tree roots will only grow where they have access to nutrients and water. Compacted soil is detrimental to tree root systems due to the lack of void space. Void space in soil allows for water and oxygen to trickle down and feed the tree roots. Void space is also needed for tree roots to grow and explore, in highly compacted soil conditions the tree root has to expend extra energy to push through the compacted soil in search for water and nutrients. We commonly see this impacting roads and sidewalks where the tree roots heave the pavement causing damage and safety concerns for the community.

Related: How to Stop Pavement Lift from Tree Roots

In a 10-year time lapse comparing trees planted simultaneously, we observe that the tree canopy of trees planted in Stratavault vastly outperformed the tree canopy of trees planted in structural soil.

What is CU-Structural Soil?

CU-Structural Soil, a patented soil mix developed by Cornell University’s Research Foundation, is engineered to foster tree root growth while bearing the load of pavements, roads, and urban infrastructure. This specialized blend offers a slightly expanded rooting area for urban street trees, effectively reducing tree mortality rates and preventing sidewalk failure due to compaction issues. For detailed insights into CU-Soil's research and application, refer to this link.

This soil mix allows for root expansion while prioritising necessary load-bearing capacity to support sidewalks and pavements, being compacted to 100% peak density. With CU-Soil, tree roots thrive, accessing vital nutrients and water without compromising the structural integrity of urban infrastructure.

Scientific studies confirm the efficacy of CU-Soil, showcasing somewhat enhanced tree health and longevity compared to conventional planting methods. Additionally, CU-Soil's contribution to LEED certification makes it a sustainable choice for projects.

Grow Better Trees with Stratavault

stratavault with raised foot plates

stratavault with raised foot plates

Stratavault is a structural soil vault system designed to support the above weight of urban infrastructure such as roads, pavement, parking lots, etc and provide void space that can be backfilled with high quality uncompacted soil which increases the growth rate of trees in urban environments.

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Download our specifier tech sheet to understand the engineering and environment benefits that using soil cells has in creating urban greenery.


Structural Soil Benefits

Structural soil was once the standard for planting trees in urban environments due to its ability to sustain healthy tree growth in challenging urban conditions when compared to fully compacted soil used in urban settings. By providing a stable foundation and some room for root expansion, it allows trees to establish themselves, withstand urban stresses like foot traffic, road traffic, and compacted soils, and ultimately grow in environments where traditionally highly compacted soil was used.

Here are some key advantages:

  1. Enhanced Root Growth: Structural soil provides a slightly improved environment for root development when compared to traditional planting. The larger coarse components in the soil create open spaces that allow roots to penetrate and expand, promoting healthy root growth. This leads to stronger, more stable trees that can better withstand environmental stresses.
  2. Improved Soil Drainage: Traditional compacted soils in urban areas often suffer from poor drainage, leading to waterlogged conditions that are detrimental to tree health, and the safety of the community. Structural soil, with its coarse composition, facilitates better water drainage, preventing excess water from accumulating around the roots. This helps prevent root rot and ensures a well-aerated root zone.
  3. Somewhat Increased Soil Volume: Urban spaces are typically limited in soil volume available for tree roots. Structural soil addresses this challenge by providing a higher volume of soil in a given area. The combination of coarse and fine components(rocks) allows for a greater amount of soil within the same space, providing more room for root expansion and nutrient uptake.
  4. Soil Compaction: Urban areas often experience soil compaction due to heavy foot traffic and construction activities. This compaction restricts root growth and limits the availability of oxygen and water. Structural soil, designed to mitigate total compaction, helps reduce the issue by maintaining its structural integrity even under pressure.
  5. Longevity and Sustainability: Structural soil is engineered to be durable and long-lasting, providing a stable growing medium for trees over an extended period. Its composition promotes long-term soil health and reduces the need for frequent soil replacement. This sustainable approach contributes to the overall longevity and sustainability of urban landscapes.

By utilizing structural soil for urban tree planting, city planners, landscape architects, and arborists can create better outcome from trees when compared to the traditional way trees of planting trees in urban settings. 

sidewalk tree being installed in structural soil

Types of Soil used in Urban Settings

When it comes to structural soil, there are various types available, each with its own unique characteristics and applications. Understanding the different options can help you make an informed decision based on the specific needs of your urban planting project. Let's explore some of the common types of structural soil:

  1. Engineered Structural Soil: Engineered structural soil is a specially designed blend of coarse aggregate materials, such as crushed stone or gravel, combined with soil components. It is engineered to provide both structural support and ample soil volume for tree root growth. This type of structural soil is often used in sidewalk planters, tree pits, and other confined urban spaces.
  2. Manufactured Soil Mixes: Manufactured soil mixes are custom-blended soil formulations that incorporate specific proportions of sand, compost, loam, and other organic materials. These mixes are designed to meet the requirements of urban tree planting, offering improved drainage, nutrient availability, and root penetration. Manufactured soil mixes are often used in larger-scale landscape projects where more flexibility in soil composition is desired.

Factors such as space constraints, project requirements, and desired outcomes will influence your choice. Consulting with landscape professionals or arborists can provide valuable guidance in determining the ideal structural soil solution for your specific needs.

How to Successfully Install Trees

Proper installation is crucial for creating a supportive environment that promotes healthy root growth and long-term tree vitality. Here are some practical tips to guide you through the installation process:

  1. Site Preparation: Before installing structural soil, it is essential to prepare the planting site properly. Start by removing any existing pavement, debris, or compacted soil that may hinder root growth. Excavate the area to the recommended depth, ensuring sufficient space for the structural soil and the tree's root ball.
  2. Soil Layering: When installing structural soil, it is common to layer it with different materials to maximize its effectiveness. Begin with a layer of uncompacted gravel or crushed stone at the bottom of the planting hole. This layer serves as a drainage system, preventing water from accumulating around the tree's roots. Above the gravel layer, add the structural soil mixture, ensuring it is evenly distributed and adequately compacted.
  3. Root Ball Integration: During the installation process, it is crucial to properly integrate the tree's root ball with the surrounding structural soil. Gently place the tree in the center of the excavated hole, making sure the root collar is at or slightly above the surrounding grade. Gradually backfill the hole with the structural soil mixture, firmly but not excessively compacting it around the roots. Be careful not to damage or disturb the roots during this process.
  4. Mulching and Watering: Once the structural soil and tree are properly installed, apply a layer of organic mulch around the base of the tree. Mulch helps retain moisture, suppresses weed growth, and regulates soil temperature. Be sure to leave a small space around the tree trunk to prevent moisture buildup. After mulching, thoroughly water the tree to settle the soil and provide initial hydration. Follow recommended watering practices to ensure the tree receives adequate moisture during its establishment period.
  5. Ongoing Care and Maintenance: After installation, ongoing care and maintenance are crucial for the long-term health of the tree. Regularly monitor soil moisture levels and adjust watering accordingly. Implement a proper pruning and fertilization regimen to support tree growth and vitality. Conduct periodic inspections to identify any signs of stress, disease, or pest infestation, and take prompt action as needed.

By following these installation guidelines and providing ongoing care, you can optimize the benefits of structural soil and create an environment where trees can thrive in urban settings. Remember, the establishment period is critical for the tree's survival, so attentiveness and proactive maintenance in the beginning stages of it's planting are key.

Interested in upskilling your team in how to design soil volumes for trees in urban areas?

Growth Comparison using Stratavault for soil and roots

Growth Comparison of the same tree using Stratavault soil cell system.

The Future of Soil for Urban Tree Planting

While Structural soil brings a multitude of benefits to urban tree planting projects it is no longer the best way to support healthy tree growth in hardscape urban environments. Soil Vault systems (soil cells) are a new technology rising in popularity around the world and case studies of plantings are starting to show the growth and environmental benefits using a soil vault system such as Stratavault have on improving the outcomes of trees in urban spaces. It's matrix design contribute to the long-term health and vitality of trees in challenging urban environments.

What are the significant advantages that soil vault systems provide:

  1. Enhanced Root Growth: One of the primary benefits of soil vaults is its ability to promote robust root growth. The open structure and ample void space within the soil matrix allow tree roots to penetrate deeply and spread extensively. This leads to stronger root systems, improved stability, and enhanced nutrient and water uptake.
  2. Reduced Soil Compaction: Urban environments often suffer from soil compaction due to heavy foot traffic, construction activities, and vehicle loads. soil vault systems addresse this issue by offering a low-compaction solution that supports healthy root growth. The 100% recycled engineered matrix design takes the structural load of the above infrastructure(not the soil or tree), providing a supportive environment for trees to establish and thrive.
  3. Improved Drainage: Proper drainage is essential for preventing waterlogged soil, which can be detrimental to tree health and can result in tree death. Soil Vaults systems are designed to include a layer of compacted gravel or crushed stone with supported drainage under the vault. When water enters the soil vault to nourish the tree, any excess water will flow out from the bottom of the vault and be directed into the supported drainage. This excess water can then be channeled into the city's infrastructure or nearby irrigation systems.
  4. Ample Soil Volume: Urban tree planting often faces space constraints, with limited soil volume available for root growth. Soil vault systems such as Stratavault solves this problem by providing a calculated soil volume within a structural matrix. The increased soil volume offers more room for root expansion and nutrient absorption, promoting healthier and more vigorous tree root growth at maturity.
  5. Longevity and Durability: Soil Vault Systems are designed to withstand the rigors of urban settings and has excellent longevity and durability. The engineered structural matrix ensures stability and strength, even under heavy traffic or pedestrian loads. This means that trees planted in soil vaults with adequate maintenance tree programs can thrive for an extended period, providing long-lasting beauty, shade, and environmental benefits.
  6. Stormwater Management: Another noteworthy benefit of soil vault systems are their contribution to stormwater management. The soil vault structure allows for the infiltration and storage of rainwater, reducing runoff and helping to mitigate urban flooding by ensuring that the water is used in the environment that it fell. This environmentally friendly feature promotes sustainable water management and supports the overall health of urban ecosystems while also reducing the burden on city infrastructure in a cost effective way.
  7. Flexibility and Adaptability: Soil Vault Systems are a versatile solution that can be customized to meet the specific requirements of different tree species and project site conditions. As soil vaults such as stratavault are modular it can be tailored to accommodate variations in project space, drainage needs, and root space requirements. This adaptability makes it suitable for a wide range of urban planting scenarios, from streetscapes and sidewalks to plazas and parks.

By harnessing the benefits of soil vaults, urban tree planting projects can overcome the challenges associated with limited space, soil compaction, and inadequate drainage.

Related Case Study: ROI of Planting Street Trees

Stratavault structural soil option for installing trees in urban environments to grow faster

Stratavault: Leading Soil Cell System Worldwide

Factors That Influence Structure Grade of Soil

Soil's structural grade is a critical factor that determines its ability to support healthy plant growth and overall ecosystem vitality. Whether it's in urban gardens or rural landscapes, the soil's structural grade influences water retention, drainage, aeration, and nutrient availability. A well-balanced soil structure fosters strong root development and contributes to the long-term sustainability of plants.

Several factors influence the structure grade of soil. These include:

  1. Organic Matter Content: The presence of organic matter, such as compost or decomposed plant material, greatly influences soil structure. Organic matter helps create aggregates or clumps within the soil, improving its overall structure and porosity.
  2. Particle Size Distribution: The distribution of different-sized soil particles affects the soil's ability to form aggregates. A balanced mixture of sand, silt, and clay particles can enhance the soil's structure by creating spaces for air and water movement.
  3. Soil Compaction: Soil compaction, caused by human activities or natural processes, can negatively impact structure grade. Compacted soil lacks pore space, restricting the movement of air, water, and root growth. It is essential to address soil compaction issues before planting trees to ensure optimal structure grade.
  4. Soil Moisture: The moisture content of soil plays a role in structure grade. Excessive moisture can lead to soil compaction, reducing pore space and affecting overall structure. On the other hand, adequately moist soil promotes the development of desirable soil aggregates.

Impact of Soil Structure Grade on Tree Health and Growth

Trees planted in soils with optimal structure grades are better equipped to establish strong root systems, access essential nutrients, and effectively manage water. Conversely, poor soil structure can hinder root development, leading to inadequate nutrient uptake and compromised water drainage.

The structure grade of soil significantly influences tree health and growth. Here are some key impacts:

  1. Root Penetration: Soil with a favorable structure grade allows tree roots to penetrate deeply and spread widely. This enables the roots to access essential nutrients, water, and oxygen, supporting healthy root development and overall tree vitality.
  2. Water Drainage: Soil with good structure grade facilitates proper water drainage. It prevents waterlogging, which can lead to root suffocation and the development of root diseases. Effective drainage ensures a healthy balance of soil moisture, promoting optimal tree growth.
  3. Nutrient Availability: Well-structured soil provides a favorable environment for nutrient availability and uptake. The presence of aggregates allows roots to explore a larger soil volume, accessing a greater pool of nutrients essential for tree growth and development.
  4. Soil Aeration: Adequate soil structure promotes air circulation within the root zone, ensuring sufficient oxygen supply to tree roots. Oxygen is vital for various physiological processes, and a well-aerated soil environment supports healthy root respiration.

By understanding the concept of structure grade in soil and its significance, tree planters can make informed decisions when selecting and preparing soil for tree planting projects. 

While understanding structural soil is key to promoting healthy tree growth in urban environments. By incorporating the right soil composition and ensuring an optimal structure grade, we can provide trees with the necessary conditions for ideal root development, efficient water drainage, nutrient availability, and adequate soil aeration. The use of soil vault systems, such as the Citygreen soil vault system, offers innovative solutions that improve the quality of urban tree outcomes and contribute to the long-term success of tree planting projects.

Remember, when working with structural soil, consider the specific needs of the tree species, the requirements of the project, and the site conditions. Adjusting the soil ingredient mixture accordingly and following a performance-based approach to soil specification can yield excellent results. Addressing factors such as organic matter content, particle size distribution, soil compaction, and moisture levels can greatly influence the structure grade and overall health of the trees.

By prioritizing the use of quality soils and implementing innovative support structures, create sustainable urban landscapes that benefit both the environment and the community. Investing in the health of our street trees and urban forests not only beautifies our surroundings but also contributes to cleaner air, improved stormwater management, and enhanced quality of life.

Book a Consult with our team to learn how you can use a soil vault in your project.

How to Grow Large Trees In Urban Environments

large trees planted in stratacell on Laman St, Newcastle NSW

To grow large trees in urban environments presents unique challenges and considerations. Urban settings often have limited space, compacted soil, and various infrastructure constraints that hinder tree growth. However, finding effective methods for nurturing substantial trees in cities is crucial for enhancing green spaces, improving air quality, and promoting overall health and well-being for urban dwellers.

Why We Need Larger Trees in Urban Environments

From combating air pollution and mitigating the urban heat island effect to fostering biodiversity and improving physical and mental well-being, larger trees play a crucial role in enhancing the overall quality of life. 

Large Trees Mitigate the Urban Heat Island Effect

Strategic placement of trees in urban areas has been proven to have a remarkable cooling effect on the shaded regions, with temperature reductions ranging between 2ºC and 8ºC. This cooling phenomenon is a result of multiple interconnected factors.

Firstly, trees provide shade through their expansive canopies, which obstruct direct sunlight from reaching the ground. By blocking the sun’s rays, trees create a cooler microclimate beneath their canopy, shielding the area from excessive heat. This is especially beneficial in densely built urban environments, where concrete and asphalt tend to absorb and radiate heat, contributing to the urban heat island effect.

Secondly, through a process called transpiration, trees release water vapor into the atmosphere. This evapotranspiration process helps dissipate heat and lowers the air temperature, further contributing to the cooling effect in the shaded areas. In addition, as water vapor is released, it can also contribute to increasing local humidity, which enhances the comfort of the surroundings.

Large Trees are Great Urban Air Filters

Large urban trees play a pivotal role in mitigating environmental pollution and enhancing air quality in urban areas. As natural filters, they possess the remarkable capacity to absorb significant amounts of air and soil pollutants, including up to 150kg of carbon dioxide (CO2), along with fine particulates

The absorption of carbon dioxide by urban trees is a crucial process in combating the escalating issue of climate change. 
This carbon sequestration not only helps mitigate climate change but also aids in offsetting the carbon footprint of urbanized regions, contributing to broader efforts in achieving carbon neutrality and sustainability.

The effectiveness of urban trees as pollutant filter is influenced by their proximity to emission sources. Studies have shown that trees in close proximity to pollutant-emitting activities absorb up to nine times more pollutants than trees situated farther away. So, strategic tree planting near busy roads, industrial areas, and other pollution hotspots is essential to maximize their air purification capabilities and create healthier living spaces.

Related: Best Tree Species for Reducing Air Pollution

Large Trees Improve Water Quality

The presence of large trees in urban landscapes has far-reaching effects on water bodies and the ecosystems they support.

One of the key contributions of large trees in urban settings lies in their capacity to manage and clean stormwater runoff. Impermeable surfaces like roads, pavements, and rooftops prevent rainwater from naturally infiltrating the soil. As a result, large volumes of stormwater rush over these surfaces, picking up pollutants such as oil, heavy metals, fertilizers, and other contaminants.

See how Citygreen integrate trees into the Stormwater Management process with our Strataflow System.

Related Stormwater Case Study: 105th Street Edmonton, Canada

Large Trees Improve Physical and Mental Health

Large trees provide a host of physical and mental health benefits. Their presence in urban environments not only fosters cleaner air but also encourages higher levels of outdoor physical activity among nearby residents, as they create a cooler and more inviting environment for exercise

On the mental health front, spending time in the presence of large trees has been linked to reduced stress and anxiety levels. Being in nature and experiencing green spaces have a calming effect on the mind, promoting relaxation and mental rejuvenation. Moreover, large trees create aesthetically pleasing environments that positively influence mood and emotional states. 

Larger Trees Improve Property Values

Larger trees significantly contribute to improving property values and are regarded as valuable assets in real estate and urban planning. The presence of well-established trees in residential neighborhoods and commercial areas adds a touch of natural beauty, reduce noise pollution, decrease crime rates, and reduce power usage due to temperate reductions. Another study also showed that, for every dollar invested in planting, cities see an average US$2.25 return on their investment each year.

Related: Soil Vaults Unlock Massive ROI For Your Trees

So, the faster tree canopies grow, the sooner the benefits can be enjoyed by cities, stakeholders and communities.

How to Plant Large Trees in an Urban Environment

Planting large trees in an urban environment requires careful planning and the implementation of effective strategies to ensure the successful establishment and long-term growth of the tree. Utilizing advanced urban forestry practices and harnessing the potential of technology like Citygreen’s Stratavault soil vault system can significantly enhance the viability and sustainability of urban tree planting.

Another crucial aspect is the preparation of the planting site. Urban soils are often highly compacted due to the need to support surround infrastructure such as pavement, roads and building foundation. Highly compacted soil is not conducive to tree growth as the soil is and lacking in nutrients, oxygen and space for growth which hinders root development . 

When growing large trees in urban environments, Citygreen’s Stratavault soil vault product proves to be a game-changer when it comes to urban tree planting. Its modular design allows for efficient and scalable tree planting in confined urban spaces. The stratavault system creates an ample underground soil volume, providing ample room for root expansion and nutrient uptake while ensuring the roots are contained within the matrix and never impact surrounding infrastructure like roads pavements, and underground utilities. This innovative technology also facilitates stormwater management, reducing runoff, stormwater capture and storage while enhancing the tree’s access to water, ensuring its resilience during dry periods.

Related Case Study: 10-year Urban Tree Growth Comparison

Another consideration when planting large trees in urban areas is the selection of suitable tree species. Opting for native or adaptive tree species that are well-suited to the local climate, soil conditions, and urban challenges is crucial. These species exhibit greater resilience to local environmental stressors, making them more likely to thrive in the often harsh urban settings.

Urban Tree Growth Case Study

At Citygreen, we love science. Since 2011, we’ve researched, developed and refined our range of sustainable urban landscape solutions to withstand rigorous testing – and produce outstanding results. So, when our Stratacell structural soil vault system became the subject of a study comparing the performance of soil treatments under concrete paving, we were keen to see the findings.

The study, entitled ‘Comparison of Soil Treatments Under Concrete Pavement’ was conducted by Thomas Smiley, James Urban and Kelby Fite at the Bartlett Tree Research Laboratory in Charlotte, North Carolina. It examined variations of the two main approaches that have been developed to provide rooting space for trees in urban areas – supported pavement and structural growing media.

Overall, the study found that structural bearing modules (like Citygreen Stratacell and Stratavault systems) grow the largest, healthiest trees in the fastest time. It also highlighted the superior all-round performance of these systems compared to others.

Study goals

The purpose of the study was to compare the growth of trees in different supported pavements and structural growing media. The aim was to determine which methodology would produce the largest, healthiest trees in the shortest time.

A key driver behind the research was canopy cover. Tree canopy provides a huge range of environmental, economic and health benefits, including:

  • Combats climate change by reducing greenhouse gas emissions
  • Provides natural shade and cooling
  • Conserves energy and reduces power costs
  • Enables water filtration and retention
  • Provides habitats for wildlife
  • Increases property and area values
  • Promotes health and wellbeing
  • Contributes to a sense of place
  • Encourages community interactions
Bartlett Study on how to Grow Large Trees In Urban Environments

SUP Trial Plot Sept 2017


To achieve the study goals, two plots were established at the Bartlett Tree Research Laboratory. The first plot was installed in 2004, exclusively for Study 1, which examined five variations of supported pavement systems. The second plot was established in 2014, specifically for Study 2, which examined six variations of structural media.

Citygreen’s Stratacell system was part of Study 2, which also included an open control, compacted control, sand based structural soil (SBSS), gravel based structural soil (GBSS) and another structural load bearing module, similar to Stratacell.

At the start of Study 2, on 19 August 2014, containerised 18mm caliper Liriodendron chinense trees were installed in the centre of each plot. A 5cm thick layer of concrete was poured over the plot, with a 20cm hole centred on each tree. A soil moisture sensor was also fitted.

Over the following three years, the trees were measured and assessed regularly against key performance indicators. On 23 October 2017, the trees were severed at the root for final measurements and findings. During the excavation, soil was removed from the roots, leaving the mass intact for examination.

5 Pressure Wash and Hydrovac blog green infrastructure expensive Citygreen

Pressure wash and Hydrovac for removal of soil from the root systems


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Airspade removing soil from around the roots


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Weighing Process of all root systems

How to Grow Large Trees in Urban Environments Key Findings

Overall, the study found that soil treatments that provided a low density growing media aka uncompacted soil (such as Citygreen Stratacell and Stratavault) resulted in the largest, healthiest trees in the shortest time. These findings were consistent across Study 1 and Study 2. However, in Study 2, the tree growth differences between the systems were more pronounced than in Study 1.

The structural load bearing systems, including Stratacell, performed extremely well in Study 2. Compared to the compacted soil, SBSS and GBSS, these systems consistently achieved the highest scores across multiple measures of tree health and growth, including:

  • Tree trunk diameter
  • Tree height
  • Foliar Colour
  • Number of roots > 1.2cm diameter
  • Maximum root spread
  • Maximum root depth
  • Weight of tree parts
  • Moisture content of soil

Stratacell outperformed all other systems in terms of maximum root depth, moisture content and foliar colour. Like the other structural load bearing module, it also produced significantly larger trees with more large roots than other treatments, including compacted soil, SBSS and GBSS.

The final findings were consistent with observations throughout the study, which reported that the trees in structural load bearing modules began to diverge from other treatments by the end of 2015. Similarly, in 2016 and 2017, there were significantly larger than most other treatments.

3 Strata left Silva right blog green infrastructure expensive Citygreen

Trees grown in structural load bearing modules


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Tree roots developed in Stratacell and Silvacell vault systems


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Root systems grown in gravel based Structural Soil


The study concluded that structural soil vault modules (such as Citygreen Stratacell and Stratavault) are superior for growing large, healthy trees in the fastest times when compared to other systems, such as compacted soil, SBSS and GBSS.

While the study did not point to a ‘best product’, it proved the methods that support the load on a pavement and keep that load off the growing media work better than those that don’t.

This is good news for urban planners, landscape gardeners, architects and developers. It means that, simply by choosing a structural load bearing soil system, they can achieve the canopy cover they require years sooner than they might with other systems.

Similarly, cities, communities and individuals can enjoy the environmental, economic and health benefits of tree canopies faster and for longer.

Have one of the Citygreen contact you. 

Contact the friendly Citygreen Team now for more information by clicking here.

Download the full report

Click here to download the full ‘Comparisons of Soil Treatments Under Concrete Pavement’ study.

How Understanding Soils and Watering Can Prevent Street Tree Failure

A new video released by Citygreen demonstrates the importance of understanding soils and watering to prevent street tree failure. Citygreen Consultant, Nathaniel Hardy, visits a stressed street tree located in the dry climate of the ACT. Despite being irrigated with a suitably large volume of water, the tree is lacking outer foliage with bare, dead branches clearly visible. So, why is the tree failing to thrive despite receiving the required volume of water?

Nathaniel draws attention to the finely-textured, clay-filled soil in the rectangular garden bed surrounding the tree. A circular mulch ring around the tree is simply not big enough to cope with the volume of water being provided, so much of the water is escaping into the larger garden bed and then onto the surrounding pavement. Because the pavement is only slightly elevated, water does not have a sufficient opportunity to penetrate the fine soil and irrigate the roots below. Instead, we see a dry, caked soil surface which has become largely impervious to water.

As the video demonstrates, simply providing the required volume of water is not enough. Understanding the character of your soil and the runoff behaviour of water provided is integral to providing an environment in which street trees can thrive.

To find out more about Citygreen’s innovative water sensitive urban landscape solutions, visit To speak to Citygreen about this video, email

Sydney Pioneers Working Urban Farm

Think working farms only belong in the country? Think again! Sydney now has its own urban organic farm, with Pocket City Farms launching in Camperdown on a former bowling green.

Seeking to provide an alternative to fast-food supermarket fare, Pocket City Farms General Manager, Emma Bowen, says, “In cities, we are often disconnected to the origins of food and the effort that goes into growing food. So we wanted to put farming in a place where people can suddenly reconnect with how food is grown again and know where their food comes from.

“Our primary aim is to bring farming into the city and to create food as locally as possible… People can come past and see us growing the food and then come in on a Saturday to our market and buy the food. It’s a real instant connection.”

Incorporating 1200 square metres of market garden growing vegetables, greens, and herbs, the farm also includes a food forest, chicken coop, and a public footpath currently under construction featuring fruit trees and other edible plants.

Volunteers help out on the farm in exchange for practical lessons on urban farming. One such volunteer is Marrickville local, Kirsty Davies, who says, “Nowadays, food is just big business. We are so used to going to the supermarkets to get food, not knowing how it was grown. But this farm is visible to the public and it raises awareness about where food comes from.

“The nutritional value in food from the big supermarkets is [often] pretty low. To see the food being grown locally makes you think about where it comes from. It would be great if we could have so much food growing around us that we wouldn’t need to be so reliant on big supermarkets.”

To find out more, visit Pocket City Farms. Or, find out more about innovative urban forests here


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