Green streets

Image credit: Stichting Open Boek

Trees need quality soil to grow

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.

Roots need room to grow

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).

Trees have specific water needs

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.

Do not allow soil compaction to occur

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.

Tree roots need adequate oxygen

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.