Soil should provide good air circulation, organic content, porosity, water storage capacity and soil biology. Soil biology should be sufficient to generate active decomposition in the ground to convert some of the compounds from the dust particles collected by the trees into harmless compounds. Remove sterile building sand and replace with the appropriate soil mixture, depending on the situation.
Prevent the ‘flower pot effect’ by providing sufficient underground growing space with suitable conditions. The size of the tree planting area depends on the surrounding uses above ground (park or yard vs. street or building), the size of the tree, and how high the water table is. At the design stage, the mature size of the tree should be considered. Excessive pruning to accommodate adjacent buildings, powerlines, etc. denies the tree its essential energy (leaves are the lungs of the tree).
Maintenance and water should be budgeted into the project to guarantee optimum growth. This is especially important in the first year after planting. Avoid digging planting beds deeper than 20cm above the groundwater table. Caution is advised in using the planting beds around trees as drainage for surrounding pavement because of the damage that may result from excess water or salt.
If too much compaction occurs under pavement (traffic areas) then root growth is limited due to less porosity, air circulation and water drainage / availability. Compacted soil restricts water infiltration into the root zone and groundwater table.
This can be achieved by the proper soil type with porosity or with a perforated pipe network with 40% perforation under the pavement. Pavement which is damaged by roots is usually caused by roots searching for oxygen closer to the surface
Create the proper growing conditions for urban trees so they are healthy and can perform optimally.
|tree soil||tree sand||tree granulate|
|organic matter||high content (5-7%)||4-5%|
|structure||open and loose||mix of coarse sand and organic matter||60% rocky material mixed with 40% compost, peat or clay|
|amount of traffic||no traffic within canopy radius||light traffic||medium to heavy traffic|
|location||open ground: parks, green areas, green strips between paving and grass/planting||under sidewalks, bicycle paths, parking||under streets (with good circulation)|
|min. points||not suitable under pavement and traffic||must be professionally mixed to avoid compaction, lack of oxygen and drying out||must be professionally mixed because it does not mix evenly, also difficult to dig holes for utility work|
“Green in the city … provide the right conditions … and nature will do the rest.”
In new development:
Remove building sand in all tree and plant beds and replace with planting soil. Design not only above ground but also underground so there is ample room for trees to grow.
In existing development:
Street renovation should not only be based on traffic circulation but also the optimal growing space for the new or existing street trees. Street profiles, space underground and soil type should be adjusted to prevent problems such as paving damage due to roots.