Turf, often called sod, is a layer of grass with a thin mat of soil and roots, harvested in rolls or squares. This material offers an instant lawn solution for home gardens and public spaces. While laying this fresh turf over an old lawn is tempting for a quick fix, experts caution against this shortcut. A new lawn’s success depends entirely on creating a healthy connection between the new root system and the existing soil, which old grass actively prevents.
The Immediate Problems of Laying New Turf Over Existing Grass
The primary issue with laying new turf directly over existing grass is the failure of new roots to establish themselves deep into the underlying soil. The old grass, including the dense layer of dead and living material known as thatch, acts as a physical barrier. This barrier forces the roots to remain shallow, making the lawn vulnerable to drought and heat stress since it cannot access deeper moisture.
The decomposing layer of trapped old grass also creates biological problems. This organic material breaks down, generating heat and fostering conditions that encourage fungal diseases and insect pests, such as grubs. Furthermore, the uneven decomposition causes the ground beneath the new turf to settle unpredictably. This results in a spongy, uneven surface prone to bumps or depressions, which creates tripping hazards and makes mowing difficult.
Minimal Preparation: When Trying to Save Time
For homeowners determined to avoid the labor of full removal, a high-risk, minimal preparation method offers only a slim chance of success. This approach begins with aggressively scalping the existing lawn down to the lowest setting to expose the soil surface. After scalping, the area should be scarified or heavily aerated to break up the dense thatch layer and perforate the soil.
The next step involves applying a thin layer of topdressing, such as a sandy loam mixture, over the entire area. This layer, typically no more than a half-inch deep, should be raked smooth to create the most direct contact possible between the new turf’s roots and the existing subsoil. This technique attempts to bypass the old grass barrier; however, it still inherits all the issues of the old lawn, including poor drainage and potential weed seeds, making it a temporary fix at best.
The Recommended Approach: Creating a Proper Soil Base
The only way to guarantee a healthy, long-lasting lawn is to prepare a proper soil base by completely removing the existing vegetation. This process begins by either using a non-selective herbicide to kill the old grass or by renting a sod cutter to physically remove the turf layer. Once the old lawn is gone, test the soil’s pH and nutrient levels to identify any deficiencies that need correction.
The underlying soil should then be tilled or loosened to a depth of four to six inches to promote deep root growth and improve drainage. This is the ideal time to incorporate soil amendments, such as compost or sandy loam, spread to a depth of at least two to four inches. A common ratio for a turf underlay is an 80% sand to 20% organic material mix, which ensures good porosity for water movement while retaining nutrients.
After amending the soil, the area must be rough-graded to establish the correct slopes for water drainage, ensuring water moves away from structures. A final, meticulous leveling with a landscape rake will remove any remaining debris and clods, creating a smooth, firm surface. This surface should be approximately one inch below any sidewalks or driveways to accommodate the thickness of the new turf. Before laying the sod, a starter fertilizer can be lightly raked into the top inch of soil, and the prepared base should be lightly moistened to prevent the new turf from drying out immediately upon contact.
Essential Care After Turf Installation
Once the turf is laid, immediate care is necessary to promote root establishment. The most important step is watering thoroughly within 30 minutes of installation, ensuring the water penetrates the sod and moistens the top few inches of the soil base. During the first seven to fourteen days, the new turf should be watered multiple times a day—often twice daily—to keep the sod and underlying soil consistently moist, but not saturated.
After the initial watering, the new turf needs to be rolled or lightly tamped to press the sod firmly against the soil base, eliminating air pockets and ensuring good soil-to-root contact. Foot traffic must be minimized for the first three weeks to prevent shifting the sod pieces or compressing the tender new roots. The first mow should be withheld until the turf has securely rooted into the soil. This can be tested by gently lifting a corner; if it resists, it is ready, typically around three to four weeks after installation. For the first cut, the mower blades should be set high, removing no more than the top third of the grass blade to avoid stressing the new lawn.