Lawn Soil Types

When we talk of soil, we are really discussing the relatively thin layer of topsoil that sits atop a much deeper layer of subsoil. The topsoil is the layer in which plants can grow; subsoil is unfit for plant growth. But the subsoil can affect the chemistry of the topsoil, most specifically, the ph. The other important factor in the makeup of topsoil is location.

Soil differs greatly from one geographic region to another, but all soil falls into one of three classifications: clay, loam, or sand. If you live in certain parts of the south, you may have to deal with distinctively clay-heavy soil, while homes in coastal areas often struggle with extremely sandy soils. Loam is the most desirable soil. Clay drains poorly and the dense structure resists root growth. Sandy soil drains much too quickly to hold the nutrients necessary to keep the lawn healthy.

No matter what type of soil is natural to your area, soil health and structure also depend on how the lawn has been used over time, and how it has been maintained. For instance, a lawn that has seen many years of hard use as a football field for a growing group of kids will likely be tightly compacted and dense. An excess of certain nutrients such as calcium can also adversely impact soil structure, as can an imbalance of other nutrients.

However, most lawn soils are not totally one type or the other. If you look closely at your soil, it’s likely you’ll see a mix, such as a sandy loam. That’s why the goal of improvements like aerating the lawn, and adding structural amendments such as compost, is to create a soil that is most conducive to a healthy lawn.

Determining Your Soil Texture

Soils partly come from the earth’s mineral crust and partly from the remains of living things. The mineral (inorganic) part is rock that has been worn down to particles. Clay (left photo) is simply stone that has worn down to microscopically small particles. Clay soils are dense and slow draining. Clay soils compact easily when wet. Compacted clay soils resist root penetration and do not support grass well. Most clay soils form a tight wad when squeezed in your hand that does not easily crumble.

The inorganic part of Loam soils (center photo) are a mixture of clay, silt, and sand particles. Loam is the best soil for lawns since it doesn’t compact like clay or dry out like sand. A handful of moist loam will form a ball when squeezed, but the ball will crumble as you handle it.

Sand soils (right photo) are gritty and resist forming a cohesive ball. Sand soil resists compaction better than clay and loam but dries out quickly unless generously amended with organic matter. Heavy clay and dry sand soils are best improved with the addition of compost or other organic matter.