Soils that receive regular foot and/or vehicular traffic tend to become compressed and dense. This compression is called soil compaction and is generally more of a problem in soil containing high amounts of clay. Because of reduced air movement between the soil and the atmosphere, compacted soils contain less oxygen and increased levels of carbon dioxide and other toxic gases. Since oxygen is needed for growth and development of turf root systems, the result is poor rooting and thin turf. Compaction also causes slow water infiltration leading to poor soil drainage. You can tell that a soil is compacted when grass growth and thinning begins in high traffic areas. The soil surface becomes hard, especially when dry, and it is difficult to force a trowel or other digging tool into the soil.
Aeration is the process alleviating soil compaction by removing small cores of soil and turf from a lawn; thus, creating a system of large pores through which moisture and air can move into the soil. This is usually done with a mechanical aerator equipped with cylindrical, hollow tines, usually about ¼ to ½ inch diameter and between 3 and 4 inches long. Many different types of lawn aerators are available and the model that ACA Lawn Care has is Ryan lawn air 28 will give you 12 holes per square feet.
Aerating equipment having solid tines or spikes does not remove cores from the soil. Although these types of aerators create pores in soil, they do not decrease overall soil compaction as the movement of soil to all sides of the hole result in a denser soil mass.
Mechanical aeration is perhaps the only means of reducing soil compaction on established lawn areas and should be performed frequently (once a year) on high – traffic areas. Usually, several passes of the core aerator over the lawn is needed to achieve noticeable improvement of compacted soil. Be aware that making many passes removes more turf, thus the lawn will become thinner. Although the turf will recover, this temporary thinning can open the lawn to weed invasion if there are significant weed or weed seed populations present at the site. You do not have to aerate as frequently or as extensively on lawns that are no heavily trafficked and on soils that contain low clay contents.
The cores that are brought to the surface can be ground-up after they have dried with a vertical mower or power rake. The remaining debris (thatch and grass plants) can be removed from the lawn with a blower or lawn sweeper. If you allow cores to remain on turf surface, they will eventually break apart due to rain and/or traffic. However, this can take several days or weeks, depending on weather conditions and the amount of traffic. In the meantime, moist soil cores can be smeared into the turf by lawn mower tires and foot traffic, resulting in some smothering and thinning of turf.
The best times to aerate lawns are in spring and late summer/early fall when soils are moist. Aeration can cause injury to grasses when lawns are under heat and drought stress or in a semi-dormant condition during midsummer. Aeration should only be performed during cool conditions (below 80 degrees F) when lawn grasses are growing vigorously.