Establishing a new lawn, whether from seed or sod, requires promoting a deep, robust root system. Applying nutrients at the correct time is paramount because young grass is highly vulnerable to chemical burn. Initial fertilization must feed the tender root zone without overwhelming the fragile new blades, focusing on root development rather than immediate top growth. Using the wrong product or fertilizing too soon can stress the developing plant and hinder the lawn’s long-term health.
Fertilizing New Grass Seedlings
New grass grown from seed requires a delicate approach, as tiny seedlings are sensitive to nutrient levels. The initial application of a starter fertilizer should occur just before or at the time of seeding to prepare the soil and ensure immediate nutrient availability for germination. This pre-application allows phosphorus to settle into the soil, where nascent roots will encounter it soon after sprouting.
The first post-germination feeding should be delayed until the grass is approximately four to six weeks old, or until the blades have reached two to three inches in height and have been mowed at least once. This delay ensures the primary root system is established enough to benefit from the fertilizer without risk of injury. A second application of starter fertilizer is recommended about 30 days after the initial seeding to sustain the rapid establishment phase.
Fertilizing New Sod, Sprigs, and Plugs
Transplanted grass, such as sod, sprigs, or plugs, already has a developed root structure, changing the fertilization timeline compared to seedlings. Sod benefits from an application of a starter fertilizer shortly after installation to help the roots knit quickly into the native soil. This initial feeding encourages the transplanted roots to grow outward and downward, securing the sod to the ground.
For sod, waiting until the new roots show evidence of successful establishment, typically around one month after planting, is common before the second feeding. Check for root knitting by attempting to gently lift a corner of the sod; resistance indicates the roots have successfully penetrated the soil beneath. Sprigs and plugs may benefit from a pre-planting fertilizer application, followed by a subsequent feeding six to eight weeks later to boost their spreading growth.
Selecting the Right Starter Fertilizer
The choice of fertilizer for new grass should focus on a product specifically labeled as a “Starter Fertilizer.” These products are formulated with a high proportion of Phosphorus (P), the middle number in the three-number NPK ratio found on fertilizer bags. The NPK ratio represents the percentage by weight of Nitrogen (N), Phosphate (P), and Potash (K).
The high Phosphorus content is important because it is the element responsible for energy transfer and lateral root growth, which new grass needs for rapid establishment. For example, a common starter fertilizer ratio might be 10-18-10, indicating low Nitrogen for shoot growth and high Phosphorus for root development. Potassium (K) assists with overall cell strength, disease resistance, and drought tolerance. Before purchasing, check local ordinances, as some municipalities restrict the use of phosphorus-containing fertilizers to prevent water runoff and pollution.
Application Techniques and Follow-Up Care
Once the correct timing and product are determined, the application process must be executed precisely to ensure even coverage and prevent chemical burn. Using a broadcast or drop spreader is the recommended method for granular fertilizer, ensuring uniform distribution across the entire area. Spreader settings should be calibrated according to the manufacturer’s instructions to avoid over-application, which can severely damage the young lawn.
Thorough watering is required immediately following the application of a granular fertilizer. Watering washes the granules off the grass blades and down into the soil, where the roots can absorb the nutrients. This step also prevents the high salt content in the fertilizer from drawing moisture out of the grass blades, which causes the characteristic brown streaking known as fertilizer burn. Following the initial establishment period, the first follow-up feeding should occur six to eight weeks after the initial application to sustain growth into a dense, mature lawn.