Excessively compacted soils can bind essential nutrients making them unavailable for uptake via tree roots. Sometimes it is necessary to utilize a tool called an air knife/spade to till the soil. The compressed air is powerful enough to work the soil but gentle enough not to damage tree roots. Compacted soils are very common in the urban environment and adversely effect tree health.
Alleviating soil compaction while incorporating compost and other beneficial organics has proven effective in improving root function and overall tree health. This practice combined with establishing a large mulch ring can drastically improve the critical root zone for valued trees. Healthy Soil = Healthy Trees