Plant roots need air. If they can’t get air, they die. So why do the roots survive underground where air isn’t seemingly available?
Soil is made up of particles of sand, silt or clay (or a mixture of them). Good soil has a good amount of pore space between the particles. This allows for air and water to move through the soil. When soil has poor structure or we mistreat it, we compact the soil. As we run over the soil when it is too wet or with equipment that is too heavy, we are pushing the soil particles closer together. As a result, the pores are small and can hold less air and water for plants. When soils become extremely compacted, roots can no longer penetrate the soil. Compacted soils have fewer and smaller roots.
The roots have to be able to continually grow and explore to find new nutrient reserves. Water needs to be able to move easily through the soil where it can reach roots and wash nutrients to where roots are. Compaction not only directly affects root growth; it also reduces the amount of air-filled pores and thus oxygen in the soil. The increase in carbon dioxide (CO2) in relation to oxygen can be toxic to plant roots.
Soil compaction can severely restrict turfgrass growth and can arise in lawns from a variety of events. Traffic over a lawn or specific areas of a lawn is probably the leading factor in soil compaction. This traffic includes human activity, pet runs or vehicular movement. Soils can also become compacted during residential or commercial construction process due to movement of heavy equipment on the lawn. Insects, diseases, nematodes, improper watering, lack of fertilizer and poor turfgrass management are often blamed for a lawn’s decline when the real culprit is soil compaction.
The best way to avoid turf problems due to compacted soils is to alleviate any compaction prior to turf establishment. However, this may not always be feasible. If the situation arises where an established turf is planted on a soil prone to compaction, consider the following tips:
Avoid continuous traffic patterns over the same turf area. This can include foot traffic, pet traffic or tire traffic.
If heavy traffic is unavoidable, remove the turf from the area and replace it with a non-turf pathway such as permeable pavers, flagstone steps or mulch.
Keep foot traffic off turf areas by using properly placed pathways and using landscape design that includes hardscape, as well as trees and shrubs, to direct traffic.
Be careful when using large, heavy mowing equipment. Change mowing patterns often and use lightweight mowing equipment when the soil is wet. Consider avoiding the use of heavy mowers altogether on compactable soils.
If a soil is compacted, the solution is straightforward: aerate.
Aeration is the practice of physically removing cores of soil and leaving holes in the lawn. Taking these plugs out loosens compacted soil and increases the availability of water, oxygen and nutrients as well as enhances the activity of thatch-decomposing organisms. While removing cores of soil, the spoons or tines also sever roots, rhizomes and stolons where the grass plants are stimulated to produce new shoots and roots that “fill up” the holes in the lawn and increase the density of the turf.
Our warm-season grasses such as zoysia, centipede, St. Augustine and bermuda are best aerated in late spring and summer, when they are actively growing. Be careful on St. Augustine and centipede because core aeration can damage the tender stolons that run on top of the ground. You can rent core aerators from a local tool rental place or have a reputable contractor save you a Saturday afternoon.
Reach Campbell Vaughn, the UGA Agriculture and Natural Resource agent for Richmond County, by e-mailing email@example.com.