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  • ASLA staff 7:42 pm on December 5, 2017 Permalink | Reply  

    Urban Street Tree Planting: Correcting Myths and Misconceptions 

    November Webinar_Jim Urban_Sugar Beach_Toronto

    ASLA 2012 Professional General Design Honor Award. Sugar Beach, Toronto, Ontario. Photo credit: James Urban

    Jim Urban’s recorded presentation “Urban Street Tree Planting: Correcting Myths and Misconceptions” is now available through ASLA’s Online Learning series. Hosted by the Planting Design Professional Practice Network, this presentation provides valuable information on best practice recommendations for urban street tree design.
    Despite 35 years of research, books, articles and lectures, the profession still maintains many myths and misconceptions about designing with trees in urban spaces. Tree health is still at risk from all too common and obsolete design errors. This webinar will point out the most common of these errors, and provide best practice recommendations to develop truly sustainable urban landscapes. Based on the six most critical concepts of designing for healthy trees, this session will teach sound, science based designs, details, and specifications. Better informed designers will have the tools to incorporate science and sustainability principles into the aesthetic principles that guide the design of these important landscape spaces.

    Learning objectives:
    • Understand best practices related to urban street tree planting.
    • Incorporate the six most critical principles to attain sustainability in urban tree design.
    • Use the latest research findings to make decisions on soil options for urban trees.

    James Urban, FASLA, ISA
    Urban Trees + Soils

  • asla staff 2:28 pm on July 5, 2016 Permalink | Reply  

    Tree and Soil Research Blog Site Launched! 

    Research supported design for soils and trees. Photo credit: James Urban

    Research supported design for soils and trees.
    Photo credit: James Urban

    For the past year, the Tree and Soil Research Subcommittee of ASLA, comprised of Jim Urban, FASLA, Chair, José Almiñana, FASLA, Eric Kramer, ASLA, and Peg Staeheli, FASLA,  has been working on ways to engage ASLA members in tree and soil research. This includes making the existing research more easily accessible to members, helping them to incorporate research into their own practice, and encouraging members to participate in new research efforts. To that end, the subcommittee, with the support of ASLA staff, is launching the Tree and Soil Research Blog to serve as a platform for discussions on tree and soil research. The site is intended to allow members to ask questions, post their own experiences related to research, develop community discussions and research-based best practices, and give researchers the opportunity to post their work for review and discussion.

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    • Carl R. Kelemen, RLA, FASLA 1:39 pm on August 21, 2016 Permalink | Reply

      Like the site. I hope to see this grow and become even more valuable. I have learned several key things that will be incorporated into my specs and construction documents already.

      Keep up the good work.


    • Carl R. Kelemen, RLA, FASLA 1:53 pm on August 21, 2016 Permalink | Reply

      Thanks for setting this up. I hope it will provide much needed information and guidance for the profession. in reading the current posts, I have already picked up some pointers that I will incorporate into my specifications and construction documents.


    • daniel straub 8:19 pm on October 5, 2016 Permalink | Reply

      Excellent… with all of the new energy associated with higher-density mixed use development, complete streets, and green infrastructure, this blog will be a very valuable resource for many. Thank you.


    • Gordon Mann 4:51 pm on October 28, 2016 Permalink | Reply

      The challenges I have observed in landscape designs are:

      The project is not designed for the mature size of the tree, rather the tree at planting. Trees are dynamic and the site will change over time, the trees will get bigger.

      There are not long term maintenance plans included for the final spacing, irrigation changes, and periodic thinning, transplanting, or removing trees not in alignment with the final design and spacing.

      While adequate soil volume meets one challenge – design for mature trees, from the maintenance perspective is missing. It is hard to remove living trees and plants even when they were placed as temporary plants as the project grows and fills in. There has to be a plan in place as the site changes over time to “allow” the removal or transplanting of plants to reach the final spacing . If the design has a life period of say 20 years, that has to be noted and divulged.


    • Lan Hogue 12:44 pm on November 10, 2016 Permalink | Reply

      Thank you for starting this dialogue! Looking forward to participating and learning from these discussions.


    • Tobi Louise Kester 7:56 pm on February 7, 2017 Permalink | Reply

      I look forward to being a pat of this conversation! The soil component of green infrastructure is critical and as yet, not well defined in terms of what plants need…everything I’m currently dealing with is first and foremost designed to infiltrate quickly – which on it face is problematic for plants! I look forward to hearing about and discussing additives like biochar and biomass, along with research into how plants change soil over time.


  • Lauren Mandel 9:59 pm on May 26, 2016 Permalink | Reply
    Tags: , ,   

    Macro to Micro: Scalable Urban Habitat 

    McCormack Post Office and Courthouse Building green roof in Boston, designed by Andropogon Associates. Photo credit J. Nystedt.

    McCormack Post Office and Courthouse Building green roof in Boston,
    designed by Andropogon Associates.
    Photo credit: J. Nystedt.

    In 1998 Leslie Sauer Jones wrote The Once and Future Forest: A Guide to Forest Restoration Strategies. Embedded within the book’s forward, landscape architect Ian McHarg implored: “We must participate, with action and all the experience we can bring” in order to attempt to reverse environmental degradation and we can no longer expect our actions to be reversed with inaction. He further suggested that we embrace, “important havens, such as the interstices of cities” as critical canvasses for habitat enhancement and expansion for our native plants and animals.

    Within our cities, large, contiguous tracts of vegetation, such as urban forests and riverfront corridors, offer critical ecological value potential. However, in more densely developed fragments of the city, where landscape design increasingly occurs, researchers are discovering that purposely selected woody plants can similarly provide animal species with viable urban habitat. Conceptualizing the ecological value of these urban interstices may be a function of perspective, or scale.

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  • James Urban FASLA 12:57 pm on May 23, 2016 Permalink | Reply

    Retaining soil structure to improve soil 

    Unscreened soil harvesting image: James Urban

    Unscreened soil harvesting
    Photo credit: James Urban

    Soil structure (how soil particles are held together to form larger structures within the soil) is recognized as an important property of a healthy soil. Grading, tilling, soil compaction and screening soils during the soil processing and mixing process damages structure.  Structure makes significant contributions to improving root, air and water movement thru the soil. Soil screening is extremely damaging to structure but is included in most soil specifications.

    Why do we screen soils and what happens if we do not? Prior to the mid 1970’s soils were rarely screened and landscape plants performed quite well.  Installed soil was moved with clumps or peds throughout the stockpile. In the last 15-20 years farmers who have stopped tilling their soil have found significant improvements in soil performance. Several new research projects suggest that elimination of the screening and tilling processes in favor of mixing techniques or soil fracturing that preserve clumps of residual soil structure may improve landscape soils.

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    • Aris W. Stalis 10:49 pm on July 6, 2016 Permalink | Reply

      This topic is near and dear to me – regardless of how much we put in specs, this is often ignored. At times, it is because earth moving is in the Civil scope, or the requirements are simply ignored. Construction managers and contractors are concerned with building construction, and ignore the site. My plan is to request photographic documentation of the process – photo, and send via email. Quick, easy, no need for reports so it will not drive up cost. Additionally, the need to be free of weed seed in compost is also a bit of a challenge – I look forward to hearing from others on that topic.


    • Paul Josey 3:58 pm on January 5, 2017 Permalink | Reply

      Great article! How can we measure soil clumps or peds and include such requirements in specification language?


    • Jim Urban 10:15 pm on January 5, 2017 Permalink | Reply

      Paul: Right now more work is needed to add metrics to ped or clump sizes and limitations particularly in specifications. We need to look at a number of soils across the soil texture range to determine what is possible. The biggest problem is that different soils types have different ability to hold peds together during harvesting, shipping and grading. Tthe greater the clay the stronger the peds, while loamy sands and sands have almost no peds. This is further compounded by moisture. In clay soils more moisture generally results in weaker peds but they can reform in the process as the clay is sticky. Less water results in stringer peds. In sandy loans what peds that exist will be stronger with more water. Silt loans are somewhat in between. finally greater soil organic matter will strengthen peds, but the peds tend tend smaller. In my area of the mid Atlantic coastal and piedmont the soils are pretty good at maintaining peds as long as you do not screen the soil. I suspect that in the central plains areas you would have the same results. The rest of the country can key off this basic understanding.
      As far as specifications, I am still using a fairly vague ped language that is primarily there to recognize if the soil has been screened. My spec reads: “Topsoil and Planting Soil shall NOT have been screened through any screen smaller than 2” square and shall retain soil peds or clods larger than 2 inches in diameter throughout the stockpile.” I would like to use a larger minimum screen size say 3″ or even 4″ but it seems that 2″ is what most soil suppliers have and the ped idea is not mature enough to expect the industry to buy different equipment. Some times other factors make some minimum screening a valid part of the process. I try to control the overall screening requirements by controlling the source stock pile approvals and looking for soil with more clay. 15- 35% clay is a good target number for a soil that will hold up under grading and handling.
      Hope this helps.
      Jim Urban

      Liked by 1 person

  • Eric Kramer, ASLA 2:56 pm on May 19, 2016 Permalink | Reply
    Tags: Eric Kramer   

    Let’s Dig: crowd-sourcing data on urban soil performance 

    A soil core of sand-based structural soil Photo credit:

    A soil core of sand-based structural soil

    Data, data, data.

    We know that all good science is based on adequate data. And if you’re reading this page, you probably also already know there is a lack of adequate data when it comes to the real-world performance of urban tree planting soils. This post is your chance to change that and add your own information to a shared database of soil performance data.

    A bit of background: In 2014 we (Eric Kramer, ASLA, and Stephanie Hsia of ReedHilderbrand; Robert Uhlig, ASLA, of Halvorson Design; Bryant Scharenbroch, PhD of University of Wisconsin – Stevens Point; and Kelby Fite, PhD of Bartlett Research Labs) undertook a micro-study of seven sites in Boston — constructed urban landscape projects anywhere from 5 to 45 years old. Each project took a pro-active approach to designed soil systems, using suspended pavements, Cornell University structural soils, or sand-based soils. We took soil cores, recorded soils horizons, took lab samples and compared findings to what we knew about what had been installed. We also assessed the performance of the trees over time.

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  • James Urban FASLA 2:56 pm on May 19, 2016 Permalink | Reply

    Nursery Standards – Rootstock Problems and Specification 

    Roots properly pruned with no roots above the root collar Photo credit: James Urban

    Roots properly pruned with no roots above the root collar
    Photo credit: James Urban

    Stem girdling roots, kinked roots, J roots, T roots, and root collars buried deeply in the root package are one of the principle reasons whey trees and large shrubs fail to recover from transplanting or decline and even die at a young age after planting. These problems are typically created in the nursery by practices that do not produce plants with radial root architecture and place the root collar close to the surface of the soil. As a plant moves thru the production process from propagation to delivery at the site, there are many opportunities for root problems to develop in the plant.

    Most plants are started in small containers and then gradually moved into larger containers. If the plant is sold in a container there may be three or four different container sizes. Each of these containers may result in a series of roots circling around the edges of the pot forming circling roots. Any of the circling roots above the root color can eventually choke the tree. Other roots may be deflected from the bottom of the container and grow upward to the surface forming a sharp kink in a root that may eventually become an important structural root. If these misshapen roots are not pruned at each shift in pot size they form an imprint of constricting roots in the next container. As trees are repotted they are also often placed too deeply in the next pot. Trees lined in the field may also be buried in the soil. This places the roots too deep in the soil where oxygen is less available at a critical point in the trees development.

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    • Aris W. Stalis 10:17 pm on July 6, 2016 Permalink | Reply

      One thing about this, is I am trying to upload image associated with discussion, and not working to well, or I just am missing something. Instead of new post, I wish to add to the discussion.


    • Aris W. Stalis 10:21 pm on July 6, 2016 Permalink | Reply

      Further trying of this tool – we find we cannot be on site for plantings. The result is a need to dig up the plants. Messy, since we disturb the “perfect mulch circle” hiding problems, but that is what we have to do to see if it was installed properly.


    • James Urban FASLA 1:12 pm on July 21, 2016 Permalink | Reply

      Bringing these ideas into the work of LA’s is going to be difficult but is not impossible. Using the referenced specifications and details will give you the basis to reject plants and get plants modified. But getting the time and fees to actually do the field inspections is the tough part. In the end it will fall to how committed is the designer to delivering sustainable quality products to their clients. But atlas the above is a start in the process and an new tool to use.


  • Lauren Mandel 1:10 pm on May 17, 2016 Permalink | Reply
    Tags: , ,   

    Urban Plants & Soil as Stormwater Management Workhorses 

    Shoemaker Green at the University of Pennsylvania, designed by Andropogon Associates with stormwater engineering by Meliora Design. Photo credit Barrett Doherty

    Shoemaker Green at the University of Pennsylvania, designed by Andropogon Associates with stormwater engineering by Meliora Design.
    Photo credit Barrett Doherty

    When high-intensity rainfall events roll through cities, particularly those with combined sewer systems, peak flows increasingly overwhelm grey infrastructure, compromise water quality, and induce sedimentation and erosion. New research suggests that engineered soil and purposely selected plants within green infrastructure may help offset these flows by offering more benefit than most stormwater engineering models and municipalities acknowledge.

    A handful of progressive entities – like the Chesapeake Stormwater Network and the Commonwealth of Virginia – now award extra stormwater credit for management approaches that deploy high-performance engineered soils, dense and varied planting palettes, or an inter-connected series of green infrastructure elements. More research is needed, however, to mobilize engineers, designers, and policy makers to rely more heavily on the “green” in green infrastructure.

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    • Lauren Mandel 2:38 pm on July 21, 2016 Permalink | Reply

      Thank you, Jim! We think this topic is relevant to urbanites and urban stormwater policy alike.


    • Trevor Kimball 9:01 pm on October 7, 2016 Permalink | Reply

      I’m not sure if this is the right place to post this, but I wanted to get some feedback on issues related to stormwater infiltration/management in planting beds along a roadway, especially in the Intermountain West region. I figured this could be a good forum to possibly get some answers.

      1. What is the right way to deal with high clay content in soil for infiltration areas? What are appropriate procedures for amending the existing soil in these types of situations?
      2. How do you deal with chemicals from roadway runoff, especially high salt concentrations from winter road maintenance on a busy street? If irrigation is in place (for use when needed), is there procedure for “flushing” these types of contaminants through the soil? Or is it simply handled by selecting the appropriate plants for the situation, with the expectation that they will be resilient enough to withstand such chemicals?

      I apologize if these seem to be simple or naïve questions. I have read a lot of information concerning green infrastructure, but don’t have a lot of experience with it and am trying to become more educated so I can have the correct approach when working on these types of projects. I would appreciate anyone’s insight who may have expertise in this area.



      • Jim Urban 5:35 pm on October 26, 2016 Permalink | Reply

        Trevor On clay soils, There is emerging research that suggest that fracturing these soils to a depth of about 24 inches and then tilling the top 8″ really increases the permeability and reduces runoff of these soils. in your area I would also apply compost when tilling. If you send me an email to I will send you the papers. On salt, your biggest issue is low rainfall means less flushing, and flushing along with good soil in the bed is critical. Be sure to include under drainage lines in all beds is the best recommendation along with using plants that have a good track record of salt tolerance.


    • Jim Urban 4:17 pm on November 28, 2016 Permalink | Reply

      Trevor: Sorry it took me so long to respond. Here is my take on your questions.
      1. Clay soil: Simply fracturing, deep tilling, ripping, lofting what ever we should be calling it will make clay soils excellent soils for infiltration. My method id to use a back hoe and dig into the soil to about 24 inches and then drop the soil back into place. There is an excellent paper on using clay soil that was presented at the ASLA conference in Chicago “Amending Site Soil to Enhance Infiltration on Compacted Urban Sites” The actual paper reference is “Controlling Storm water Quality and Quantity by amending soils for enhanced infiltration on construction sites in North Carolina Richard McLaughlin et all April 28, 2014. This study only looked at runoff and they were not looking at plant growth. I would add a 3” layer of compost to the fractured soil and surface till it to improve plant growth if the soil is low in organic matter (less than 2% in my areas but in the intermountain areas a much lower SOM may be fine. A second study Below Ground Matters: Urban Soils rehabilitation increases tree canopy and speeds establishment, Lyman et all Urban Forestry & Urban greening, 16 (2016) 25-35, looks at a similar soil fracturing concept on tree growth. This paper did not look at infiltration but there is a strong link between infiltration and plant growth. If you get one you will get the other. There are several other research projects that examine reuse of existing soils on other soil types.
      The easiest way to get the papers is to send me an email to and i will send you copies ( and anyone else who responds to this post).
      2. Chemicals from road ways particularly salt. There is a section in my book “Up by roots” on salt (pare 64-65 and 314) that should guide your thinking on a wide range of salt issues. The most simplistic answer I can offer is that you need to identify the extent of the problem. I find for example that in dense retail environments where normal road salt and sidewalk salt are combined with additional salt spread by business owners the problem is the most severe and a multi range approach is needed. Road soil by itself is not too severer if the soil is well draining an not compacted. This can most often be felt with by better plant choices. But road salt that becomes airborn and drifts can impact a wide range of plants.

      Hope this helps.
      Jim Urban


      • Trevor Kimball 6:09 pm on January 11, 2017 Permalink | Reply

        Thanks for your reply, I appreciate your input! I will send you an email to get the papers you mentioned, that should be helpful.


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