Lawn aeration in the fall provides several benefits for your grass. Grass roots have a very difficult time penetrating the heavy clay soils that exist in this region. Core aeration helps open up areas in the clay for the roots to expand, and for moisture, nutrients and air to get down to the roots. Without aeration, often lawns become so compacted that the water and nutrients just run off, and roots are slow to expand beyond the first few centimeters down into the soil.