Urban Tree & Planter Backfill Custom Blends for Stability, Porosity, and Water Holding
Urban trees have a very difficult environment in which to try to thrive and grow to maturity. In addition to heavier concentrations of vehicle exhaust, higher ambiant air temperatures, reflected heat from building glass, and sometimes higher wind velocities from nearby skyscrapers, the most aggrevating conditions usually relate to the root zone growing medium, especially the common lack of porosity - lack of air and water access to the roots.
Starting at the soil surface, most urban trees are lucky to have a 4 foot or 6 foot square tree grate surrounding the trunk to protect roots from compaction and allow air and water entry to the root zone. This is critically small when the common street tree would normally have a root system 20 to 30 feet in diameter in non-urban situations. Thus, air and water have access via suface areas of only 16 to 36 square feet instead of 300 to 700 sf. Little wonder that street trees are often stunted and/or very slow to grow.