Laying a new lawn requires careful preparation, and the short answer to whether you can simply lay new turf over old grass is generally no. This shortcut is strongly discouraged because the existing organic layer compromises the foundation and long-term success of the new surface. Whether installing a living lawn or a permanent synthetic surface, the established plant material underneath must be removed to ensure proper rooting, stability, and drainage. Preparation varies significantly depending on the type of surface being installed, making it important to understand the differences between natural and artificial turf.
Defining Natural Sod Versus Artificial Turf
The term “turf” refers to two completely different products with distinct installation needs. Natural sod is a harvestable product consisting of live grass, its root system, and a thin layer of soil. It is a biological product that requires direct contact with prepared soil to establish a deep, functional root structure for a living, self-sustaining lawn.
Artificial turf is a manufactured textile made of synthetic fibers designed to mimic grass. It is an inanimate surface that does not require soil or nutrients. Its stability and function depend entirely on a non-organic base layer that provides a firm foundation and efficient water drainage. Because it is synthetic, it cannot root into the ground and must be secured to a compacted, engineered sub-base. These differences dictate the unique preparation steps necessary for a successful installation.
Immediate Problems with Laying New Sod Over Old Grass
Attempting to install new natural sod directly over an existing lawn creates a barrier that prevents the new grass from thriving. The new sod’s roots must penetrate the underlying soil to access water and nutrients, a process hindered by the old grass and its dense root system. This existing layer acts as a thick thatch that shallow roots struggle to grow through, resulting in poor establishment and vulnerability to stress. Without deep soil contact, the sod remains shallow-rooted and susceptible to drying out quickly.
The old grass beneath the new sod will inevitably die and decompose, creating an uneven and spongy surface over time. As this organic matter breaks down, it leads to surface irregularities, causing bumps and hollows that make the lawn difficult to mow. The dead grass layer can also act like a sponge, holding excess moisture against the bottom of the new sod. This trapped water prevents proper drainage, potentially leading to fungal diseases, rot, and localized puddling, which compromises the health of the newly installed grass.
Laying new sod over old grass can also perpetuate pre-existing issues, such as diseases, weeds, or pests, which easily transfer to the new sod. The old root systems compete with the new grass for water and soil nutrients, further weakening the new sod’s ability to establish itself. For these reasons, the existing grass must be completely removed before proceeding with a new natural sod installation.
Essential Base Preparation for Natural Sod Installation
The correct procedure for installing natural sod requires completely removing the existing lawn and preparing the underlying soil to maximize root growth. This process begins by stripping the entire area of all old grass, weeds, and debris. Removing this material eliminates the competition barrier and ensures the new sod makes direct contact with the native soil beneath.
Once the area is clear, the soil should be tilled to a depth of approximately four to six inches to loosen the earth and improve aeration. Tilling breaks up compacted soil, allowing water and air to move more freely for deep root penetration. Soil amendments, such as compost or topsoil, and a starter fertilizer should be mixed into the tilled soil to enrich it for immediate root development.
The final step involves grading and leveling the prepared area with a rake to ensure a smooth, even surface. A slight slope away from structures should be established for proper water runoff. Achieving a firm, level finish by lightly rolling or tamping the soil prevents future surface irregularities once the sod is installed. This preparation allows the new sod’s roots to anchor quickly and deeply, transitioning it into a successful, permanent lawn.
The Critical Need for Sub-Base for Artificial Turf
The installation of artificial turf requires an entirely different foundation than natural sod, relying on a compacted, layered sub-base for stability and drainage. The existing grass and topsoil must be excavated to a depth of three to four inches before any synthetic material is introduced. This excavation accommodates the thickness of the engineered base layers and ensures the final turf height is appropriate.
A permeable weed barrier fabric is then laid over the excavated soil to prevent future organic growth from penetrating the synthetic turf. The primary component of the sub-base is a layer of crushed aggregate, such as Class II road base or crushed granite, spread to a depth of approximately three inches. This material compacts tightly to create a solid, stable foundation that will not shift or sink.
The crushed stone base must be thoroughly compacted, often to 90 to 95 percent density, using a plate compactor. It must also be graded with a slight slope to promote efficient drainage. Water must be able to filter through the turf and the base layer to prevent pooling. Laying artificial turf over existing grass causes failures, including an uneven, spongy surface, poor drainage, and the rapid degradation of the turf’s backing material.