A soft, spongy, or unstable feeling when walking on the lawn indicates a structural imbalance in the turf environment. This sensation, often described as walking on a waterbed, results from excess material or moisture accumulating near or within the soil layer. The underlying cause is usually one of a few identifiable problems preventing the lawn from maintaining a firm connection to the earth. Diagnosing the issue requires understanding the soil physics and the organic matter beneath the grass blades.
Saturated Soil and Poor Drainage
The most immediate cause of a squishy lawn is soil saturation, occurring when the ground cannot drain water quickly enough. This is often tied to soil composition, particularly high concentrations of clay particles. Clay soil resists percolation, leading to waterlogging and a persistently soft surface after rainfall or irrigation. If the soil remains saturated for more than a few hours after heavy rain, it signals a significant drainage problem.
Compacted soil, often caused by heavy foot traffic or machinery, reduces the space between soil particles, preventing air and water movement. This lack of oxygen can suffocate grass roots, contributing to the lawn’s decline and spongy texture. If standing water persists for 12 or more hours, compaction and poor drainage are the likely culprits.
To address drainage, core aeration is recommended to remove small plugs of soil, relieving compaction and increasing turf porosity. For heavy clay soils, incorporating organic matter like compost helps aggregate fine particles, creating larger spaces for water to drain. Improving the lawn’s surface grading, ensuring the ground gently slopes away from structures, is a long-term solution to promote natural runoff.
Excessive Thatch Layer Buildup
A distinct cause of sponginess that feels more “springy” than “soggy” is an excessive layer of thatch. Thatch is a dense layer of dead and living organic material, including grass stems and roots, that accumulates between the soil surface and the grass blades. While a thin layer offers insulation, a buildup exceeding one-half inch acts like a giant sponge.
This thick thatch absorbs and holds moisture, preventing water from reaching the underlying soil. The saturated organic layer compresses underfoot, creating the characteristic spongy, unstable feel. Excess moisture trapped in the thatch also creates an environment conducive to disease and pests.
Thatch often builds up due to over-fertilizing with high-nitrogen products, promoting rapid growth that outpaces natural decomposition. Certain grass types that spread via stolons are also more prone to developing a dense thatch layer. When roots grow into the thatch layer to access trapped moisture, the sponginess becomes more pronounced.
Remediation involves mechanically removing the excess organic material through dethatching or power raking. Core aeration helps less severe cases by pulling soil plugs onto the thatch, introducing beneficial microbes that assist in breaking down the debris. Dethatching should occur when the grass is actively growing, such as late summer or early fall, allowing the lawn time to fully recover.
Damage from Subsurface Pests
The activity of underground pests can contribute to a lawn’s soft or unstable texture. The most common culprit is the white grub, the larva of various beetles like the Japanese beetle. Grubs feed on the fine root hairs of the grass, severing the turf’s connection to the soil.
With a significant grub infestation, the grass feels soft and can often be lifted or rolled back easily, much like a loose piece of carpet. This occurs because the root system anchoring the turf has been eaten away. To check for grubs, peel back a small section of turf and look for the C-shaped, creamy-white larvae in the top few inches of soil.
Moles, which are insectivores, also create soft spots by tunneling extensively beneath the surface in search of food. These raised, subsurface tunnels cause the ground to feel unstable and collapse when stepped on. Their burrowing disrupts the soil structure and loosens the turf, leading to localized squishiness. Addressing the pest issue, through targeted treatment for grubs or trapping for moles, is necessary to allow the roots to re-establish and firm up the turf.