The Mill Creek neighborhood and the rest of Philadelphia are part of the Eastern Deciduous Forest Biome. In the absence of urban development and other large-scale human disturbance, the area would be a forest dominated by hardwood trees. Some trees native to the undisturbed woodland are able to survive in the harsh urban environment. Others, however, are stressed, produce less foliage and fruit, fail to reach their full potential height, and live shortened lives.

• Select species that are appropriate for site conditions, i.e., soil, climate, and hydrology.
• Choose mixtures that will grow well together, modeled on naturally occurring associations of grassland and woodland plants.
• Beware of commonly planted urban-hardy species that cause problems in particular situations:
  
  -Oak, beech, hornbeam, and ash grow large and may block out sunlight, obscure views, and interfere with overhead wires and cables.
  -Poplar and willow have a high water uptake and shallow spreading roots that can block underground pipes, dry out clay soils, and cause buildings to crack.
  -Silver maple is fast growing but has weak wood and numerous surface roots.
  -Ailanthus is fast growing and messy, with prolific flowering and fruiting litter.
  -Bradford pear has poor branching habit that leads to storm breakage.
  -Siberian elm has weak branches and is prone to beetles.