St. Augustine sod is a popular warm-season turfgrass known for its thick, coarse texture and deep green color, offering a dense lawn for warm climates. Successfully establishing this turf relies heavily on practices during the initial weeks following installation. This establishment period is a delicate phase where the sod must transition to a self-sustaining lawn. Proper fertilization timing is a determining factor for success because it directly influences the development of a robust and deep root system. Applying the right nutrients at the correct moment encourages the sod to anchor firmly into the underlying soil.
Immediate Post-Installation Timing
The question of when to apply the first fertilizer is often the most pressing for new sod owners. Immediately after installation, the sod’s primary goal is to recover from the stress of harvest and transport. The plant focuses energy on root initiation, not on producing leaf blades. Applying a granular fertilizer too early, particularly within the first week, risks chemical burn to the delicate roots and leaf tissue.
A waiting period allows the sod to settle and begin knitting its roots into the prepared soil. The optimal window for the first granular fertilizer application is typically between 10 to 14 days after the sod has been laid. This timing avoids root burn but supplies elements that stimulate aggressive root growth.
The goal of this application is to encourage the downward growth of roots, improving the sod’s ability to draw water and nutrients from the soil beneath. Delaying fertilization past three weeks can stunt the establishment process. Providing this targeted nutrient boost supports the transition to a permanent lawn structure.
Essential Nutrients for Root Growth
The chemical composition of the initial fertilizer is as important as the timing of its application. For new St. Augustine sod, the focus must be on phosphorus (P), the middle number in the fertilizer’s NPK ratio. Phosphorus plays a direct and non-negotiable role in stimulating root growth and cell division, making it the most important macronutrient for establishment. A starter fertilizer with high or balanced phosphorus, such as a 15-15-15 or 10-20-10 ratio, is recommended if a soil test is unavailable.
The nitrogen (N) content, the first number, should be low to moderate and preferably slow-release. High nitrogen encourages rapid top growth, diverting energy away from deep root development. Using a slow-release source minimizes the risk of foliar burn while providing a gentle, sustained feed. Potassium (K), the third number, contributes to overall plant health, stress tolerance, and disease resistance, and should also be included.
It is crucial to avoid any products labeled as “weed-and-feed” during this initial establishment phase. The herbicides in these combination products can severely damage the new, vulnerable root system. A safe application rate for a starter fertilizer is usually around one pound of the product per 100 square feet, but always follow the specific instructions on the product label.
Schedule for Continued Development
Once the initial two-week establishment phase is complete and the sod has received its first targeted feed, a strategic schedule is necessary for sustained, robust growth. The subsequent fertilization cadence shifts from focusing on root establishment to supporting both root depth and top growth density. The second fertilizer application should typically occur about 30 days after the initial post-installation feeding.
Subsequent applications should be planned for approximately every 6 to 8 weeks during the active growing season, extending through late spring and summer. At this point, the nutrient focus shifts away from a high-phosphorus starter formula to a more balanced maintenance fertilizer. Ratios such as 3-1-2 or 4-1-2 (e.g., 15-5-10 or 16-4-8) are recommended for established St. Augustine turf. These ratios provide a higher proportion of nitrogen to support vigorous lateral growth and deep green color.
The final feeding of the growing season, applied around 60 to 90 days after the sod was laid, should be a slow-release formula that prepares the grass for cooler temperatures. This last application helps the turf store carbohydrates, which are energy reserves that aid in winter survival and support a strong emergence in the following spring. By adhering to this phased schedule, the new sod is successfully guided to a healthy, well-rooted, and mature lawn.