Over time your soil naturally becomes compacted, leaving subsoil undesirable for healthy lawn growth.
Walking, playing, mowing and watering compact particles and reduce the air space necessary for root growth. Compaction is greatest in the upper 1 to 1 1/2 inches of soil and needs to be relieved by mechanical aeration. This mechanical process puts 2-3 inch deep, finger size holes into the soil. This improves the air, water and nutrient exchange with the root system. Overseeding is also recommended at this time.