A lawn that feels thick or spongy underfoot often results from a combination of factors, including the grass species’ genetic makeup and poor management practices. Excessive density can stem from a physical buildup of dead organic material, over-fertilization, or the natural, vigorous spread of certain grass types. Understanding the root cause is the first step toward achieving a healthy, manageable turf density.
Natural Growth Habits and Species Identification
The natural growth habit of your grass is the primary determinant of its density and spread. Turfgrasses are categorized into two types based on their growth structure. Spreading grasses use horizontal stems (rhizomes underground, stolons above-ground) to colonize new areas, creating dense sod. Examples include Kentucky bluegrass, Bermuda grass, Zoysia, and St. Augustine grass. These spreading mechanisms make the lawns naturally robust and dense.
By contrast, bunch-type grasses like perennial ryegrass and most fescues thicken by producing new vertical shoots called tillers directly from the crown. If your lawn contains large, coarse clumps, it may be invaded by a bunch-type grass, such as coarse tall fescue. These grasses grow outward from the base, forming isolated tufts that create an uneven and overly dense appearance. Identifying your main grass species is crucial because management differs significantly between spreading and clumping types.
The Impact of Excessive Thatch Buildup
A primary reason a lawn feels spongy or overly thick is the accumulation of excessive thatch. Thatch is a tightly interwoven layer of dead and living organic matter that builds up between the soil surface and the green grass blades. While a thin layer (about one-half inch) is beneficial for insulation and moisture retention, anything thicker becomes detrimental.
An excessive thatch layer creates a soft, springy feeling when you walk across the turf. This dense mat prevents the proper movement of air, water, and nutrients into the soil. Consequently, grass roots begin to grow within the thatch layer itself rather than deep into the soil. This shallow rooting makes the grass vulnerable to drought and heat stress. Furthermore, the dense, moist environment created by thick thatch is an ideal habitat for turf diseases and insect pests. The organic matter also acts as a physical barrier, preventing applied fungicides or pesticides from reaching the soil surface.
Over-Nourishment and Mowing Errors
Cultural practices, particularly fertilization and mowing, directly influence lawn density and thickness. Applying too much nitrogen-heavy fertilizer causes a rapid, soft growth flush, encouraging lush, yet structurally weak, top growth. This excessive growth rate overwhelms the soil’s ability to decompose organic matter, significantly contributing to thatch buildup.
Over-fertilization also causes the grass to prioritize blade growth over root development, resulting in a shallow-rooted system prone to stress and disease. The grass becomes dependent on constant inputs, leading to a cycle of dense growth.
Mowing errors further compound density problems. Cutting the grass too short (scalping) stresses the plant and causes shallow roots. Improper mowing leaves excessive clippings that add to the thatch layer. Allowing the grass to grow too tall between mows forces the plant to produce wider, coarser blades, resulting in a rougher, thicker texture.
Physical Interventions for Density Control
To physically manage and reduce excessive lawn thickness, several corrective actions are necessary, starting with removing accumulated organic matter.
Dethatching
Dethatching, often done with a power rake, uses vertical blades to slice into the turf and pull the thick layer of thatch to the surface for removal. This process is effective for heavy thatch problems but should be timed during the grass’s peak growth season to ensure rapid recovery.
Core Aeration
Core aeration uses hollow tines to pull small plugs of soil and thatch from the ground. This action relieves soil compaction, allowing air, water, and nutrients to penetrate the root zone efficiently. The process also introduces oxygen and soil microbes into the thatch layer, which accelerates the natural decomposition of organic debris.
Verticutting
For aggressively spreading grasses like Bermuda or Zoysia, verticutting (vertical mowing) is the most targeted approach for density control. A verticutter uses rotating vertical blades to slice through and prune the horizontal stolons and rhizomes. This process breaks up the dense network of runners, effectively thinning the grass and encouraging more upright growth. Verticutting is the primary method used to prevent horizontal spread from becoming unmanageable.