Slow Aging by Planting more Trees


Does Planting Trees Slow Aging?


Green park trees

In an increasingly urbanized world, where more than half of the global population resides in cities, the importance of urban green spaces cannot be understated. Parks, green roofs, and community gardens offer not only aesthetic appeal but also critical ecosystem services. A recent study in ScienceAdvances has documented the potential benefits of urban greenness for healthy aging, including improved cardiovascular health and reduced mortality rates. While physical activity and social interactions have been suggested as potential pathways linking greenness to health outcomes, the underlying molecular biological mechanisms remain unclear.

Epigenetic modifications, such as DNA methylation levels, have emerged as a promising avenue for understanding the link between environmental exposures, health conditions, and aging. Accumulated exposure to environmental factors can lead to DNA hyper- or hypomethylation, ultimately influencing human health. Epigenome-wide association studies have identified regions of DNA methylation that are associated with residential greenness and are implicated in physical activity, mental health, metabolic diseases, and neoplasms. DNA methylation-based biological age, known as epigenetic age, has been proposed as a predictive marker for age-related health outcomes.

Previous studies have established associations between epigenetic age and cardiovascular disease, cancer, and mortality, as well as various lifestyle and exposure factors. However, the relationship between greenness exposure and epigenetic age has been understudied, with only one cross-sectional study conducted thus far. Furthermore, no studies have examined the role of race and sex in the association between greenness and epigenetic age, which is crucial for understanding and reducing disparities in greenness exposure and its associated benefits.

To address these gaps, the findings explore the associations between long-term greenness exposure and epigenetic age, considering race, sex, and neighborhood deprivation as effect modifiers.



Characteristics of Study Participants

Over 900 participants were included, with a mean age of 45.3 years. The cohort consisted of 376 Black participants and 548 white participants, with 453 men and 471 women. Approximately 54.5% of participants had parks within a 5-km radius of their residential address. The mean Normalized Difference Vegetation Index (NDVI) value within the 5-km buffer radius 1 year before the Year 20 visit was 0.38 . Participants with parks within 5 km had slightly lower NDVI values  compared to those without parks . Moderate correlations were observed for epigenetic age acceleration.

Association between Greenness and Epigenetic Aging

Their analysis revealed a significant association between 20-year exposure to greenness, and epigenetic aging. Greater greenness was associated with slower epigenetic aging, suggesting a potential protective effect of urban green spaces on the aging process. However, when considering racial disparities, we found that Black participants had less surrounding greenness compared to white participants.

This disparity in greenness exposure led to an attenuated association between greenness and epigenetic aging in Black participants, compared to white participants. This highlights the need to address and reduce disparities in greenness exposure among different racial groups.

Furthermore, the association between greenness and epigenetic aging was influenced by neighborhood socioeconomic status. Participants living in disadvantaged neighborhoods showed a stronger association between greenness and epigenetic aging, with compared to less disadvantaged neighborhoods. These findings underscore the importance of considering neighborhood characteristics and socioeconomic factors in understanding the relationship between greenness and epigenetic aging.



The results of the study provide valuable insights into the associations between urban greenness and epigenetic aging. The observed relationship between greater greenness and slower epigenetic aging suggests that urban green spaces have the potential to promote healthy aging and mitigate the effects of biological aging processes. This aligns with previous research highlighting the benefits of green spaces for cardiovascular health, mental well-being, and overall mortality reduction.

However, it is crucial to acknowledge and address the existing inequalities in greenness exposure. The findings also highlighted the greenness gap between racial groups, with Black participants experiencing lower levels of greenness compared to their white counterparts. This highlights the need for equitable distribution of green spaces and environmental resources to ensure that all communities can access the health benefits they provide.

Neighborhood deprivation, characterized by lower socioeconomic status and limited resources, may exacerbate the impact of environmental exposures on health outcomes. Recently at our event 'Where the Shade hits the Pavement' Dr. Kim Loo spoke about the link between lack of environmental exposure and the health effects of at risk people and why efforts should be directed toward promoting green infrastructure and urban planning strategies that prioritize the creation and maintenance of green spaces in disadvantaged areas.

Overall, the study contributes to the growing body of evidence supporting the role of urban greenness in healthy aging. By understanding the complex interplay between greenness, epigenetic aging, and social determinants of health, we can inform policies and interventions aimed at creating more equitable and sustainable urban environments that promote the well-being of all individuals.

Read the full report.


Key Takeaways

Inequalities in Urban Greenness and Epigenetic Aging:

  • The study examines the association between 20-year exposure to greenness and epigenetic aging in a large, biracial (Black/white), U.S. urban cohort.
  • Greater greenness is associated with slower epigenetic aging.
  • Black participants have less surrounding greenness and a weaker association between greenness and epigenetic aging compared to white participants.
  • Participants in disadvantaged neighborhoods show a stronger association between greenness and epigenetic aging compared to those in less disadvantaged neighborhoods.
  • Urban green space provides critical ecosystem services and potential benefits to healthy aging, including better cardiovascular health and lower mortality.
  • Long-term exposure to greenness has a relationship with slower epigenetic aging, with different associations observed based on race and neighborhood socioeconomic status.

The study suggests that greenness exposure in urban areas is associated with slower epigenetic aging, but the relationship varies by race and neighborhood socioeconomic status. Black participants and those in disadvantaged neighborhoods experience lower levels of surrounding greenness and have attenuated associations between greenness and epigenetic aging. Understanding these inequalities and their implications can help inform efforts to reduce disparities in greenness exposure and promote equitable access to the health benefits of urban green spaces.

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.


vlcsnap 2023 06 22 11h23m16s243 street trees Citygreen

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

How to Manage Stormwater Sustainably

An article published online by editor and writer Melissa Denchak highlighted some shocking stormwater statistics coming out of America. Denchak stated that ‘an estimated 10 trillion gallons of untreated stormwater runoff, containing everything from raw sewage to trash to toxins, enters U.S waterways from city sewer systems every year, polluting the environment and drinking supplies… [with] runoff causes significant flooding as well.’ (Denchak 2022). 

Denchak described the ‘U.S Environmental Protection Agency (EPA) estimates that upgrading the stormwater and other public water systems will require at least $150 billion in investment over the next two decades. 

This problem is not unique to the U.S, it is a problem all over the globe. The question is, how do we address the issues caused by stormwater runoff?

In this article, Citygreen will argue that green infrastructure offers a cost-effective solution to handling flooding and stormwater pollution. 

To start, let’s break down the basics. 

Why is Green Infrastructure Important for Managing Stormwater? 

Green infrastructure sets out to replicate the circular economy of the natural environment. Attempting to mirror the efficient and self-renewing processes found in nature.

In urban settings, green infrastructure encompasses a variety of water management practices, such as treepits, planted verges, bioretention pits, swales and other measures that capture, filter, and reuse stormwater. Essentially, green infrastructure replicates natural hydrological processes using soil and plants to slow down, recycle and clean stormwater runoff.

Green WSUD stormwater mangement

What is Stormwater Runoff?

Stormwater runoff is the product of a rain event causing water to flow across the land into sewers and waterways. With the expansion of our bustling cities and the widening sprawl of our urban areas, there are more impermeable surfaces than ever, increasing the intensity of stormwater runoff.

According to Denchak, ‘the average city block can generate more than five times as much runoff as a forested area of equal size’ (Denchak 2022). 

circular economy of water

What is an Example of a Successful Green Infrastructure Project? 

Denchak proposed that New York’s Staten Island Bluebelt was the ‘first and largest green infrastructure project in the U.S.’ A rapid increase in population size saw the Island struggling to deal with sanitary waste and stormwater runoff.

The Bluebelt project ‘helped solve these issues by preserving streams, wetland areas, and other drainage corridors (Bluebelts) that use natural mechanisms to capture, store, and filter stormwater’ (Denchak 2022). Nowadays, the Bluebelt comprises more than 14,000 acres and can temporarily hold and filter as much as 350,000 gallons of rainfall. 

WSUD water drain feeding water into the tree soil vault

How does Citygreen Implement and Manage Stormwater Projects?

Over the past three decades, Citygreen has made significant investments in stormwater infrastructure projects. We learnt early on that mimicking natural systems to manage rainfall, is the most cost-effectively way to deal with stormwater runoff.

An example of a green infrastructure design that Citygreen has developed is the Strataflow™ system.  Instead of a traditional bioretention basin, Citygreen’s Strataflow™ uses an underground structural soil vault system, which delivers a high standard of stormwater treatment with a completely natural look. To any passer-by, what you see is a healthy, flourishing tree surrounded by a grassy verge, but beneath the ground is an advanced WSUD(water sensitive urban design). 

sustainable stormwater management soil cell

This design starts with a traditional drain or catch basin or the Strataflow Kerb Inlet; this device sits in the road kerb alignment, retaining the inherent structure of the concrete kerb. The inlet has a grate (acting as a screen) to stop larger-sized pollutants from entering the system, which inhibits healthy tree growth. 

The inlet lets water from the road carriageway flow through the front grate of the drain at a capacity of up to 18 litres/ 5 gallons per second. This allows the inlet to minimise pollutants entering waterways and reduce flood risks by controlling the stormwater flow entering our city’s underground drains. 

strataflow kerb inlet sitting in the kern

When the water flows through the street, it enters through the inlet and flows underground. From there, the stormwater reaches the advanced structural soil cell system, where the stormwater is stored, filtered and distributed effectively for the benefit of urban trees and proper stormwater management.

The inlet ensures the water drains down at the correct optimal depth beneath the pavement height. From there, the stormwater reaches the structural soil cell system and the tree’s root system, where the stormwater is stored, cleaned and distributed effectively to increase urban tree growth and proper stormwater management principles.

animation of how strataflow works to benefits stormwater usage

Essentially, Strataflow™ utilises readily available stormwater rather than potable water to irrigate street trees, which improves the vitality of trees and reduces the impact of stormwater and stormwater contaminants on the local environment, all while maintaining a high natural presentation. 

Stormwater Management Case Study

Pemberton is a small mountain town located 20 minutes North of world-renowned ski resort Whistler in Beautiful British Columbia, Canada.

In 2019 the town of Pemberton was awarded a government grant to upgrade ageing infrastructure and give their tourist town a facelift. Pemberton had some issues with flooding which they were keen to fix and at the same time wanted to create an inviting and enjoyable experience for the visitors and residents of the town.

One of the solutions was the Stratavault system, this system was placed underneath all sidewalks for two reasons. The first was to collect the mass of snow run off and rainfall that would typically flood the town, slow this water down and clean it with the soil held in the Stratavault system then push excess water into a nearby pond where it could be used for irrigation purposes throughout the town. The second was to hold enough soil so the trees that were planted in urban environments could have access to nutrient-rich soil for many years to come.

Book a Citygreen Consultant

Looking for a cost-effective and sustainable stormwater solution? Contact our friendly Citygreen Team today.

Are Green Living Walls Challenging to Maintain?

A common concern with green living walls is maintenance, which may put people off investing in this high-value asset – but don’t be afraid!

At Citygreen, we can provide continual support from installation to maintenance requirements for our Citygreen™ Living Wall system so consumers know they are getting the best return on their investment.

Below we have answered the most common concerns people have when they think about living green walls.

Or book an initial free consult with our Green Living Walls expert Grant Radbourne who has over 10 years in delivering green walls over all the world.

living walls Q & A

Do living walls create water damage to my building?

The Citygreen™ Living Wall systems have a waterproof membrane that prevents water from penetrating substructures.

Do living walls use too much water?

Compared to other greenspaces, the water usage for living walls like Citygreen’s™ Living Wall system is low, as it typically requires two litres per square metre per day to irrigate the wall.

Irrigation is the most critical part of a successful living wall system. In our Citygreen™ Living Wall system, we have designed the vertical irrigation lines to be embedded in a moisture retention layer for optimal water efficiency.

An optional recirculated irrigation system can be installed to achieve further water-saving outcomes.

Will a living green wall work in my ‘space’?

Citygreen’s™ Living Wall system is available in nine standard panel sizes; however, it can also be engineered to retrofit walls on unique buildings. The system is also the lightest on the market, weighing only 35kg per square meter, fully planted and saturated. This means that no additional support structures will be required on small-scale projects.

Also, as discussed above, wherever on the wall the system will be mounted does not require additional waterproofing, as a waterproof membrane is included in the design.

Do living walls require too much ongoing work?

The Citygreen™ Living Wall system comes with remote control monitoring. An advanced automated system ensures the consumer can control the system’s moisture, temperature, ph levels and general conductivity on their computer or phone. This remote capability extends to the automated refilling of the water tanks connected to the wall.

Liquid fertilizer concentrates can also be used in the automated irrigation system to feed the plants. This means that the consumer can easily maintain plant health, but they can also control the pace and vigour of new growth.

Are living walls too expensive?

Citygreen can provide a detailed cost estimate, ensuring that the most suitable living wall solution aligns with your budget.

Are living green walls too hard to set up?

At Citygreen, we will perform a site analysis to determine if any technical installation requirements will be required. For example, if we believe that the indoor installation site is too dark, we recommend using artificial lighting, which we can also deliver and install.

Depending on the site’s location: indoors, outdoors, small-scale, or commercial scale, Citygreen will also assist with plant selection to help find the best species that will thrive into the future.

Assistance will also continue past the set-up stage to the maintenance process, as Citygreen can help will pruning and any ongoing concerns and issues that the living wall may have post-construction.

An example of living walls

 Call us Today 

As shown above, Citygreen is an expert in every phase of the design and implementation of living green walls– reach out to Citygreen for a Design Workshop today.

The Role of Trees in Stormwater Management

WSUD tree design with stormwater entering a soil vault tree pit

In built-up urban areas, trees can help restore pre-development water flows and remove pollutants and filter water. Trees act as natural filtration machines, which can hold, release, and clean water through soil and evaporation.

A question often asked regarding urban trees and water capture is, can stormwater runoff from roads be too polluted for the trees to use?

Yes, stormwater can be very polluted, as large amounts of debris, particulates, and rubbish can suffocate a tree and prevent water and nutrients from reaching the tree’s root system for absorption.

Gross pollutants, such as plastic rubbish or vehicle parts, can largely be filtered out often by screens, like stormwater grates.

Smaller than gross pollutants are total suspended solids (TSS). TSS refers to solids suspended in water or wastewater that can be trapped by a filter. TSS can include various materials, such as silt, decaying plant and animal matter, industrial wastes, and sewage. High suspended solids concentrations can cause many problems for stream health and aquatic life.

Then there are soluble or water-borne pollutants, which are difficult to filter out economically. These pollutants can cause severe damage to ecosystems.

Storm water systems can be installed, which prevent these pollutants from accumulating in our water streams. Citygreen offers a revolutionary range of stormwater management solutions that prevent water pollution and make it easier –and more affordable–to manage and re-use stormwater.

Why use Trees for Stormwater Management?

Trees offer a large value add when compared to traditional stormwater management systems. Trees for stormwater management offers numerous advantages in urban areas. Firstly, trees act as natural water managers by absorbing excess rainwater, mitigating the risk of flooding and erosion. Their extensive root systems serve as filters, trapping and breaking down pollutants present in stormwater, which ultimately improves the quality of water entering local water bodies. Additionally, trees reduce the volume of stormwater runoff, easing the burden on municipal drainage systems. Moreover, these green giants contribute to urban cooling by providing shade and releasing moisture through transpiration, enhancing the overall urban microclimate and conserving water by reducing evaporation from impermeable surfaces.

Case Study: Urban Trees for Shade & Stormwater Management at Kinsmen Sports Centre in Edmonton

Furthermore, the aesthetic and social benefits of urban trees are noteworthy. Well-maintained green spaces with trees enhance the quality of life for urban residents and promote community well-being. Trees also create habitats for wildlife, contributing to urban biodiversity and ecological balance.

Engaging communities in tree planting and maintenance fosters a sense of ownership and responsibility. From an economic perspective, effective stormwater management with trees can lead to cost savings by reducing the need for extensive stormwater infrastructure. Lastly, utilizing trees that align with regulatory compliance, as many cities and regions have specific stormwater management requirements where integrating trees into stormwater management strategies not only addresses practical concerns but also contributes to the creation of attractive, sustainable, and resilient urban environments.

How Do Trees Clean Stormwater?

Trees play a vital role in filtering water through a series of natural mechanisms. Their root systems, for instance, engage in a process called root uptake, where they absorb water from the soil, including groundwater and rainwater. This not only helps in managing excess water in urban areas, reducing the risk of flooding and waterlogging, but also contributes to water purification. As water moves through the soil surrounding tree roots, it undergoes natural filtration. The soil acts as a powerful filter, capturing impurities, sediments, and pollutants present in the water, thereby improving water quality. Microorganisms in the soil and on tree roots further aid in this process by breaking down organic matter and pollutants into less harmful substances.

Additionally, trees are proficient at nutrient uptake, extracting essential nutrients from water for their growth. In doing so, trees indirectly remove excess nutrients like nitrogen and phosphorus, common water pollutants. Some tree species excel at phytoremediation, absorbing and storing pollutants such as heavy metals and chemicals, thus contributing to water purification and helping prevent water pollution.

Trees release water vapor through transpiration into the atmosphere, mitigating local flooding risks by reducing runoff volume. Trees also help retain sediments and prevent erosion, which can lead to waterbody sedimentation and, consequently, improved water clarity. Altogether, trees collectively enhance water quality by naturally reducing contaminant levels, pollutants, and sediments, making a significant positive impact on the health of water systems.

Case Study: Pelican Waters

pelican6 street trees Citygreen

Pelican Waters, a residential estate located on the Sunshine Coast of Queensland, Australia, has been trialling Citygreen’s Strataflow™ system with so far great success.

This new development aimed to use the advanced water-sensitive urban design (WSUD) and improve sales of lots near bioretention basin. Research has shown that preserving natural features in residential developments can increase the value and sale price of lots.

Instead of a traditional bioretention basin, Citygreen’s Strataflow™ uses an underground structural soil cell system, which delivers a high standard of stormwater treatment with a completely natural look.

To any passer-by, what you see is a healthy, flourishing tree, surrounded by a grassy verge, but beneath the ground is an advanced WSUD.

pelican9 street trees Citygreen

The Strataflow™ is a specialised design ‘hybrid’ tree pit, combining the best urban forestry for sustained and healthy tree growth with fully functional stormwater management – including filtration and flow management.

These designs may start with the Strataflow Kerb Inlet. This device sits in the road kerb alignment, retaining the inherent structure of the concrete kerb. The inlet has a grate (acting as a screen), to stop larger-sized pollutants from entering the system, which inhibits healthy tree growth.

rdfhbndfxh e1658458809141 street trees Citygreen

The inlet lets water from the road carriageway flow through the front grate of the drain at a capacity of up to 18 litres/ 5 gallons per second. This allows the inlet to minimise pollutants entering waterways and reduce flood risks by controlling the stormwater flow entering our city’s underground drains.

When the water flows through the street, it enters through the inlet and flows underground. From there, the stormwater reaches the stratavault system, where the stormwater is stored, filtered and distributed effectively for the benefit of urban trees and for proper stormwater management.

The inlet ensures the water drains down at the correct optimal depth beneath the pavement height. From there, the stormwater reaches the structural soil cell system and the trees’ root system, where the stormwater is stored, filtered and distributed effectively for the benefit of urban trees and for proper stormwater management.

Essentially, Strataflow™ utilises readily available stormwater rather than potable water to irrigate street trees, which improves the vitality of trees and reduces the impact of stormwater on the local environment, all while maintaining a high natural presentation.

pelican2 street trees Citygreen
Growth comparison of trees planted in Strataflow (left) and trees planted in grass verge (right)

Call us today

Looking for a cost-effective and sustainable stormwater solution? Contact our friendly Citygreen Team now by clicking here.

What is the Best Urban Tree Planting System?

When planting trees in urban areas, there are a few specific elements to consider. The first and most important thing to consider is that healthy trees require an adequate supply of loose, well-aerated, and uncompacted soil to thrive. This enables tree roots to obtain enough nutrients, oxygen and water so trees grow to their full potential in cityscapes.

In urban environments, where soil compaction is essential to provide safe support for sidewalks, roads, buildings, and pavements, a natural conflict arises when considering the planting of trees. This conflict arises because trees and their roots thrive in loose, uncompacted soil. Over the years, various methods have been employed to address this challenge and create suitable, uncompacted soil for urban trees. Among these methods, two primary practices have gradually emerged: structural growing media and supported pavement systems.

What is Structural Growing Media?

Structural Growing Media, otherwise known as Structural soil are soil mixes designed to be fully compacted to support vehicles whilst allowing tree root growth. An example of a structural growing media is the Cornell Mix, which combines rock and soil.

In developing and researching this specific mix, Grabosky and Bassuk (1996) found that there was about 30% void space in a mixture of 1.9 cm diameter crushed gravel, which could be filled with clay loam soil. Creating a stone matrix and suspending soil within the matrix pores meant that the larger diameter rocks would lock together and allow for full compaction, while soil would remain loose for root growth.

Is Structural Media Good for Trees?

While structural media can offer many benefits for urban trees, one drawback is that the actual volume of soil available for tree growth is typically less than what you’d find in a natural, uncompacted environment. This limitation can restrict the potential size and reach of a tree’s root system, impacting its overall health and stability. Urban trees face competition for space, which can limit their ability to access essential nutrients and water.

Therefore, in situations where ample space and natural soil conditions are available, traditional planting in natural soil may provide a more generous and unrestricted environment for tree growth. However, it’s essential to weigh these considerations against the benefits structural media offers, such as improved soil quality and the ability to plant trees in otherwise challenging urban spaces. Careful planning and maintenance can mitigate these limitations and ensure that trees thrive in urban environments.

Ashfield Civic Rock Soil 1 street trees Citygreen

What is Supported Pavement?

On the other hand, supported pavement systems involve engineering an underground solution for tree roots such as Stratavault so that pavement can be placed over uncompacted soil without impacting the soil quality and compaction of the soil below. Implementing a load-bearing bridge with low-density soil beneath ensures that the trees rooting space cannot become heavily compacted.

Why Use Supported Pavements for Trees?

Supported pavements are designed and used for the following reasons when it comes to trees:

  1. Root Protection: It serves as a protective layer for tree roots in urban areas. Tree roots can be sensitive to soil compaction and disturbance caused by heavy foot traffic or vehicular loads. Supported pavement provides a buffer zone that safeguards the roots from damage.
  2. Pedestrian Safety: Supported pavement ensures a level walking surface, reducing the risk of tripping and falling due to protruding tree roots. This promotes pedestrian safety, especially in areas with heavy foot traffic.
  3. Urban Infrastructure: In cityscapes, trees often coexist with various infrastructures such as sidewalks and roadways. Supported pavement helps manage tree roots, preventing them from disrupting or damaging these vital urban elements.
  4. Tree Health: By maintaining healthy soil conditions beneath the pavement in a separate contained environment such as those provided by soil cells, supported pavement allows trees to thrive in ideal growth conditions. Designed correctly it facilitates trees access to essential nutrients, water, and oxygen, promoting robust tree growth and longevity.

Studies have found that any system that allows trees to grow in non-compacted, low-density soil media will have the most excellent chance of achieving healthy tree growth (Rahman, 2013, Fite et al., 2014, Urban and Smiley, 2016).

StrataVault Soil Loading 3 street trees Citygreen
Workers placing high quality soil in a stratavault soil vault matrix

Case Study: Comparison of Soil Treatments Under Concrete Pavement

One such study that Citygreen took part in was titled ‘Comparison of Soil Treatments Under Concrete Pavement’, conducted by the Tree Research Laboratory in Charlotte, North Carolina. The research compared tree root growth using supported pavement systems and structural growing media.

In the study, Citygreen’s Stratacell systems were tested. These structural soil vaults are modular units assembled below pavement level, which meet load-bearing requirements and provide a large volume of uncompacted soil for root growth.

barlett 1 street trees Citygreen

The studies showed that the trees growing in these supported pavement treatments with low-density soil media had significantly more significant growth and generally appeared healthier.

So What is the Best Urban Tree Planting Method?

While the study did not point to a ‘best product’, it proved that structural load-bearing modules like Citygreen’s Stratacell and Stratavault systems provide the best results in urban areas, where compaction is a real issue. What this means for urban planners, landscape gardeners, architects, and developers are that by simply choosing a structural load-bearing soil system, they can achieve the canopy cover they require years sooner than they might with other systems. Essentially, cities, communities and individuals can enjoy the environmental, economic and health benefits of healthy canopies’ growth faster and for longer.

Have Someone from Citygreen contact You

For more information about our products and how we can help you create greener, more liveable cities, contact our friendly Citygreen Team now by clicking here.

Download the full report

To read more about how our system performed the best in terms of maximum root depth, moisture content and foliar colour, you can download the complete ‘Comparisons of Soil Treatments Under Concrete Pavement’ here.

Download free study report


Fite, K., E. Kramer, B. Scharenbroch, R. Uhlig, 2014. Beyond the Great Debate: Assessing Post Installation Manufactured Soils Performance. Presentation ASLA Annual Meeting, Denver, CO, USA. Grabosky, J. and N. Bassuk. 1996. Testing of Structural Urban Tree Soil Materials for Use, Under Pavement to Increase Street Tree Rooting Volumes. Journal of Arboriculture 22:255-263. Rahman, M. A. 2013. Effect of pit design and soil composition on the performance of Pyruscalleryana Street Trees in the Establishment Period. Arboriculture & Urban Forestry 39:256-266. Smiley, TE., Urban, J., and Kelby Fite, K. Comparison of Tree Responses to Different Soil Treatments Under Concrete Pavement. Arboriculture & Urban Forestry. Nov2019, Vol. 45 Issue 6, p303-314. 12p. Urban, J. and E.T. Smiley. 2014. Evaluation of Established Trees – Structural Soils and suspended pavement – Presentation at the International Society of Arboriculture Conference Milwaukee, WI, USA.

How to Promote Deeper Root Growth and Drought Tolerance

Best Tree Root Development

illustration of root growth with perforated piping for water and air

Sufficient oxygen, water, soil and nutrients are essential for healthy root growth and therefore healthy trees. If soil gets too wet, the voids between soil particles become filled with water and the root hairs cannot absorb oxygen. Over time the roots ‘drown’ which eventually may also kill the tree, through lack of the required water and nutrients.

The water from efficient tree irrigation is required not only for all the biochemical processes involved in photosynthesis, respiration and transport but also for mechanical support to leaf and stem tissue.  Insufficient (or inefficient) tree watering will result in loss of leaf turgor and a consequent reduction in new shoot extension. Eventually, this will lead to die-back and, if not remedied, the loss of the tree.

Oxygen may also be available at depth if the soil is not compacted and the action of earthworms has created tunnels through which oxygen can flow. Tree roots will grow near the surface unless adequate water and air are available below ground.

perforated piping installed around a tree to help enable deeper root growth

How to Promote Deeper Root Growth?

One method for getting tree roots to grown down is providing both the necessary water and air to the tree roots which ensures deeper root growth involves the use of a perforated flexible piping system like the Snorkil RootRain system by Citygreen. At the time a tree is being planted, the pipe may be looped around the root ball within the immediate rooting zone of the new tree, and also in the outer rooting zone, looped throughout the root cell matrix. The pipe is then connected to an inlet located at the tree pit surface. This method may be adapted for use beside roadside verges and open space tree planting or in heavily-trafficked areas.

It’s important to remember that after planting to water the rootball directly as the tree only benefits from what its tree roots can reach.

How to get tree roots to grow down?

03 Garden inlet perpespective 00000 1 street trees Citygreen

Tree roots only grow in areas that have nutrients, water, and oxygen that’s why generally speaking tree roots stay in the top 18 – 24 inches of soil depth as infiltration from oxygen and water starts to lessen.

Adding a perforated piping system to the tree roots like a Snorkil root rain can ensure that oxygen and water can easily access tree roots at a deeper depth and guide the trees deeper into the soil away from the surface.

The water inlet

The inlet enables a water hose to be attached when water is needed. The rest of the time the pipe, being looped in a circuit, allows air to flow passively through the system and around the roots of the tree. Changes in air pressure above ground are also accommodated. This arrangement enables long deep watering over the entire root system and the opportunity for the soil to dry between watering, which is better for trees and root growth than frequent light watering.

Snorkil™ RootRain

garden single 4th view cropped street trees Citygreen

RootRain™ Urban is a large capacity irrigation system with a fixed non-removable grid inlet. The grid allows water and air through but prevents ingress of litter and debris.

Suited for: Roadside verge and open space tree planting. 

Snorkil™ Rondo & Plaza Series

plaza kit single 4th view street trees Citygreen

The Snorkil™ Rondo (round inlet) and Snorkil™ Plaza (square inlet) series have been specially designed to interlock with our range of integrated tree grilles or be set in the pavement to provide an attractive and durable way of maintaining aeration for tree root systems.

This provides a tamper-resistant system that will also prevent the inlet from sinking as a result of any soil settlement around the tree.

Suited for: Integrated tree grilles or to be set in the pavement.

Why we should recycle Thermoplastics for Green Infrastructure

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As practising “green building” professionals, we are all constantly searching for the best materials for our projects. The selection of building materials that are well-engineered, cost-effective and ecologically-sound is a process that defines our effectiveness and ultimately the success of our projects. We all know how challenging it is to stay ahead of the “technology curve”, and that our understanding of the latest innovations in materials is critical to the realization of results that meet or exceed industry standards and the needs of society in general.

Technological advances in the design and production of recycled plastic “green” building materials provide us with opportunities to “push the envelope” with respect to the three important criteria mentioned above. Up-to-date and accurate information is the key to being positioned to take advantage of advances in green building materials. The following article first steps back slightly to examine the primary concepts behind the role of recycled plastics in green infrastructure projects, then looking at more-specific applications and the future of plastics, so that we all may be completely informed in our choices going forward.

What are Thermoplastics?

Also known as “engineering plastics”, thermoplastics comprise a group of materials that exhibit superior mechanical and thermal properties in a wide range of conditions over and above more commonly used commodity plastics and other materials. The term usually refers to thermoplastic (softer) materials as opposed to “thermoset” (harder) plastics. Engineered thermoplastics are typically used for parts rather than containers and packaging. A thermoplastic is made from polymer resins that can be reheated and reshaped repeatedly. These important characteristics allow the manufacturing process to be reversible, therefore making most thermoplastics recyclable.

Why Recycled Thermoplastics?

  • Recycled plastic provides a sustainable source of raw materials to the green manufacturing and building industry.
  • Reduction of environmental impacts, such as greenhouse gas emissions, associated with the production of new plastic-rich products.
  • Greatly reduces the amount of plastic entering the primary waste stream, thus sparing our already overcrowded landfills.
  • Reduction in consumption of the world’s limited natural resources, i.e.: oil.
  • Recycled plastic production represents far less “embodied energy” than the production of new, virgin polymer products.
  • Recycling in general promotes sustainable lifestyle choices.
  • Recycled plastic parts lower the cost of product manufacturing and transportation (shipping).
  • Thermoplastic products can be recycled again and again, whereby effectively closing the “lifecycle loop” of the resource.

What is Green Infrastructure anyway?

Depending on which particular interest group is defining it, green infrastructure has been used to refer to everything from innovative green roofs, to more ecologically-sensitive stormwater management systems, to large integrated networks of natural areas. What these different interpretations have in common is the essential recognition that our built environment and our ecological environment are irreversibly connected and closely interrelated.

When the term is used at a smaller scale, such as an urban park or streetscape, our working definition can be an interconnected system of man-made landscapes, natural areas and open space that preserves and enhances the sustainability of the ecosystems promotes clean air and water, and significantly benefits people and wildlife. It should be pointed out that green infrastructure at the smaller; “implementation-level” involves the design, manufacture and installation of the best possible components of the physical systems, such as tree grates, structural soil cells, permeable pavement, drainage systems, etc.

Some other informative definitions of green infrastructure are:

“Green infrastructure can be considered a conceptual framework for understanding the “valuable services nature provides the human
environment.” At the national or regional level, interconnected networks of park systems and wildlife corridors preserve ecological function, manage water, provide wildlife habitat, and create a balance between built and natural environments. At the urban level, parks and urban forestry are central to reducing energy usage costs and creating clean, temperate air. Lastly, green roofs, walls, and other techniques within or on buildings (and building sites) bring a range of benefits, including reduced energy consumption and dramatically decreased stormwater runoff. Regardless of scale, green infrastructure provides real ecological, economic, and social benefits.”

American Society of Landscape Architects 

“As communities develop and climate patterns shift, stormwater management needs can only be expected to grow. While single-purpose grey stormwater infrastructure is largely designed to move urban stormwater away from the built environment, green infrastructure reduces and treats stormwater at its source while delivering many other environmental, social, and economic benefits. These benefits not only promote urban livability but also add to the bottom line.”

US Environmental Protection Agency

birds eye view of green infrastructure in an urban city

The Benefits of Green Infrastructure

Green infrastructure systems protect and restore naturally-functioning ecosystems and provide a framework for future development. These systems provide a wide range of ecological, social, and economic functions and benefits, such as cleaner air and water, restoration and conservation of natural resource processes, enriched habitat and enhanced biodiversity, increased recreational and transportation opportunities, improved human health, and better connections to nature. Well-designed and implemented man-made and natural green spaces have proven to increase property values and significantly decrease the costs of public infrastructure and public services.

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The Benefits of Recycled Thermoplastic Materials

  • Durability-recycled plastic building products have proven to be extremely resistant to harsh environmental conditions. Plastic does not have to be painted, resists corrosion, and can be engineered to be incredibly strong.
  • Non-toxic-recycled plastic materials/parts will not leach undesirable chemicals into the environment.
  • Lower production costs-recycled and repurposed plastics are far more cost-effective than using expensive virgin polymer resins.
  • Lower shipping costs-plastic materials typically weigh less than other materials (wood and steel for example) thus transportation costs are lower.
  • Reduced environmental impacts (reduced embodied energy)-it simply requires less overall energy to produce, transport and installs recycled plastic products.

Some specific Applications of Recycled Plastic in Green Infrastructure

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LEED Credits for Recycled Plastic Materials

LEED (Leadership in Energy and Environmental Design) offers credits for the use of recycled products, including recycled plastics, in buildings, site development and landscaping in their highly regarded green building rating system.

Specifically, products like Citygreen Stratacell and Stratavault Systems may qualify your project for generous contributions toward LEED certifications, with recycled content being a high contributor. Contact for more information regarding their products and LEED credits.

Visit for more information and proposed changes to LEED rating systems.

The Future of Plastics and Green Infrastructure

The future “Greening of Plastic” doesn’t stop with the efficient recycling of a petroleum-based resource. Advances in science are forthcoming that will further revolutionize the way we manufacture and use plastic. The development of “organic plastics” or Polypropylene Carbonates (PPCs) is moving forward, and in the near future, plastics will be made from the combination of carbon dioxide and propylene oxide. This new product will perhaps eliminate the need for petroleum-based plastics altogether while utilizing a largely unwanted and ecologically-harmful element. Whether transparent, flexible, or rigid, PPC is poised to become the revolutionary product of the plastic world, and in a few short years, can be mass-produced by the chemical giant BASF.

Plastic, no matter the source, will continue to be a major factor in improving the durability and energy efficiency of future green infrastructure. The continued use of recycled thermoplastic materials will undoubtedly result in significant reductions in the overall carbon footprint of infrastructure development around the world.

Stratacell street trees Citygreen
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“We are big on compliance on all projects, and the fact that their SmartCertify cloud platform covers all bases, and supports their 20 year warranties, is critical – especially that these pits are being installed under roadways and footpaths.”

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"I reviewed all the previous projects that we have installed in the past couple years using your product and I can happily report back that we have 0% mortality in the soil cells, which is incredible!"

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