Installing new sod provides an instant lawn, but this immediate appearance of maturity can be deceiving. The grass must first successfully transition from a harvested product to a rooted part of your landscape. The first mowing is arguably the most critical step in this establishment process, as premature or improper cutting can severely damage the immature root system. Understanding the difference between the visual readiness of the grass blade and the subterranean readiness of the roots is key to a healthy, long-term lawn.
Initial Preparation and Root Establishment Checks
The first focus after installation must be on facilitating root knitting, where the new turf anchors itself to the native soil. This involves a rigorous, short-term watering regimen aimed at keeping the sod constantly moist, similar to a wet sponge, without becoming saturated. For the first one to two weeks, water the sod multiple times a day, ensuring moisture penetrates the soil beneath the turf layer to encourage downward root growth. As the first week concludes, gradually reduce the frequency of watering while maintaining the moisture level to promote deeper root development.
Once the grass blades begin to lengthen, the “tug test” becomes the primary indicator that mowing is possible. To perform this, gently lift a small corner of the sod. If the piece resists and stays firmly in place, the new white rootlets have begun to knit into the underlying soil. If the sod lifts easily, the installation is not yet secure enough to withstand the weight and vibration of a mower, and waiting is necessary. Mowing before this subterranean establishment is complete risks tearing the sod pieces apart, disrupting root growth and creating an uneven surface.
Criteria for Determining the First Cut
While a common timeframe for the first cut is 10 to 21 days after installation, the height of the grass, not the calendar date, is the deciding factor. The grass must reach a height of approximately 3.5 to 4 inches before cutting. This height ensures enough leaf surface area remains to support the young plant through photosynthesis after the trim. The most important rule is the “One-Third Rule,” which dictates that you should never remove more than one-third of the grass blade’s total height in a single mowing session.
If the grass grows too tall before the first cut, removing the required one-third may still result in a finished height that is too low. Cutting too low, known as scalping, places excessive stress on the immature root system and can inhibit new growth. For instance, if your grass reaches four inches, the highest recommended cut is about 1.3 inches, bringing the finished height down to 2.7 inches. To prepare for the cut, withhold irrigation the day before you plan to mow, allowing the grass blades to dry and the soil surface to firm up.
Proper Technique for the Initial Mowing
The execution of the first cut requires careful attention to the equipment and process to prevent damage to the newly knitted roots. Ensure the mower’s blades are extremely sharp, as dull blades will tear the delicate young grass rather than slicing them cleanly. Tearing creates a ragged wound that leaves the plant susceptible to disease and diverts resources away from root development for healing. Using a lightweight push or standard rotary mower is preferable to a heavy riding mower, as the reduced weight minimizes soil compaction on the soft ground.
Set the mower deck to its highest setting, typically three inches or more, to adhere to the One-Third Rule and avoid cutting too deeply. When beginning the cut, change the direction of mowing from the way the sod was originally laid, such as mowing diagonally across the seams. This alternate direction helps prevent the wheels from creating ruts along the sod lines and reduces the chance of lifting or shifting the edges. If the clippings are sparse and short, they can be left on the lawn to return nutrients to the soil. If the clippings are heavy or clumped, they should be bagged and removed to prevent smothering the young grass and blocking sunlight.