Sod consists of pre-grown grass and the soil held together by its root system, offering an immediate solution for establishing a lawn. Many homeowners seek to install this new turf directly over an existing lawn to save time and labor associated with complete removal. Successfully installing sod over existing grass requires specific preparatory steps to ensure the new roots establish correctly in the underlying soil structure. This guide outlines the necessary actions for achieving a healthy, lasting result.
Assessing Existing Conditions
Installing new sod directly onto a thick, living layer of existing grass is strongly advised against by turf specialists. The underlying turf actively competes with the new sod for moisture, sunlight, and soil nutrients, starving the shallow, developing root system. This competition hinders the new sod’s ability to penetrate the underlying ground, leading to poor establishment.
A dense layer of living grass also creates an uneven and unstable foundation for the sod. This results in air pockets between the sod’s root mat and the soil beneath, preventing the necessary soil-to-root contact required for water transfer and nutrient uptake. If the existing turf is thick and vigorous, total elimination is necessary; if it is sparse or dead, preparation steps can be less intense.
The decay of underlying organic matter generates heat and releases gases, which can inhibit new root growth or encourage fungal pathogens. Therefore, laying sod “over existing grass” inherently involves killing the existing grass first to prepare the site. Failure to eliminate the existing vegetation significantly increases the probability of sod failure and patchy growth.
Preparing the Base Layer
The initial step involves eliminating the existing turf using a non-selective systemic herbicide, such as glyphosate, to ensure complete root death. This chemical is absorbed by the foliage and translocates throughout the plant structure, preventing regrowth. If using a chemical method, a waiting period of 7 to 14 days is required to allow the herbicide to fully cycle through the plant and confirm complete death.
Once the existing grass is completely brown, the area must be scalped by mowing at the lowest possible setting. This removes the bulk of the dead organic matter, preventing excessive decomposition beneath the new sod layer. The remaining dead thatch should be raked away to expose the underlying soil surface, improving soil-to-root contact.
If the underlying layer of dead material is minimal, lightly tilling the top inch of soil can help integrate the remaining organic matter and improve aeration. Following this light disturbance, inspect the area thoroughly to remove any buried rocks, roots, or large debris. A smooth and consistent subgrade is necessary for a uniform final appearance.
Apply a thin layer of specialized topsoil or compost mix, ranging from one-half to one inch in depth, to provide a nutrient-rich bed for the new roots. This material ensures the sod’s initial root growth encounters optimal conditions for rapid establishment and improves the soil’s water-holding capacity.
The final step involves meticulously leveling and grading the entire area using a landscape rake or a soil screed. Proper grading ensures surface water drains away from structures at a minimal slope of two percent, preventing future waterlogging. Compacting this new layer slightly with a roller or plate compactor ensures a firm, stable base before the new turf is installed.
Laying the New Sod
Installation should begin along a straight edge, such as a driveway or patio, to establish a clean boundary. The pieces of sod are unrolled and laid down, ensuring they are pressed firmly against the prepared soil surface. Working from the installed edge prevents excessive foot traffic on the newly laid turf.
Subsequent rows must be laid in a staggered, brick-like pattern. This prevents long, continuous seams that are prone to drying out or shifting, distributing tension across the surface. Ensure the edges of adjacent pieces butt tightly against each other without overlapping.
Overlapping edges create air pockets that cause localized drying, while wide gaps lead to noticeable seam lines. Excess sod can be cut to fit edges and curves using a sharp utility knife or a spade, ensuring all pieces fit snugly.
Immediately after installation, the entire area must be rolled using a water-filled lawn roller set to a moderate weight. This action presses the sod’s root mat firmly against the base soil, eliminating trapped air pockets and maximizing root-to-soil contact.
Ensuring Successful Rooting
The newly installed sod requires immediate and thorough watering to prevent desiccation of the shallow root system. Saturate the sod and the top inch of the underlying soil until the turf is visibly spongy, which settles the sod onto the base layer.
For the next 10 to 14 days, the watering schedule should shift to frequent, shallow applications, often two to four times daily depending on conditions. The objective is to keep the sod moist without creating standing water, encouraging roots to seek moisture deeper. After the initial two weeks, gradually reduce the frequency and increase the duration to promote deeper root development.
Foot traffic should be strictly limited during the first establishment phase, ideally for the first three weeks, to avoid dislodging the root system. The first mowing should occur only after the roots have firmly knitted into the new soil, typically 7 to 10 days after installation, when the sod resists being lifted gently at the corners.