The application of lime, fertilizer, and grass seed together is possible, but success depends on significant conditions. While combining the application saves time, the decision must be guided by a soil test and the use of correct product formulations. Proceeding without these precautions can severely inhibit seed germination and waste product.
Understanding Soil pH and Lime’s Role
Soil pH, measured on a scale from 0 to 14, indicates the acidity or alkalinity of the soil, with a reading of 7.0 being neutral. Most turfgrasses thrive in a slightly acidic to neutral range, typically between 6.0 and 7.0, where nutrient availability is optimized. Lime is not a fertilizer; it is a soil amendment containing calcium carbonate that is used to raise the pH level in overly acidic soil.
Applying lime is a long-term strategy because it does not change the soil chemistry instantly, often taking three to six months to fully neutralize acidity. This slow reaction rate means it generally will not harm the newly sown seed upon contact. Pelletized lime is the preferred form for simultaneous application because its granular nature allows for easier, more even spreading and less dust.
Choosing the Right Fertilizer for Seeding
Standard lawn fertilizers contain high nitrogen (N) for mature grass growth. This high nitrogen content creates a high salt index, which can draw moisture out of delicate grass seed and emerging roots, causing fertilizer burn.
Instead, a specialized product called “starter fertilizer” must be used when seeding a lawn. Starter fertilizers are formulated with a higher concentration of phosphorus (P), the middle number in the N-P-K ratio, such as 10-20-10 or 18-24-12. Phosphorus is crucial for the development of strong, deep root systems, which is the primary goal for establishing new turf. Avoiding “weed and feed” products is also imperative, as the included herbicides will kill the germinating grass seed along with any weeds.
Applying Lime, Fertilizer, and Seed Together
The direct answer to simultaneous application is yes, provided the correct products are chosen and the soil test indicates only a minor pH adjustment is needed. A soil test dictates the exact amount of lime required; never apply more than 50 pounds per 1,000 square feet in a single application. Using pelletized lime and a starter fertilizer significantly reduces the risk of chemical interference.
The recommended procedure involves layering the materials on the prepared soil, starting with the heaviest product. First, apply the pelletized lime evenly across the area using a broadcast spreader. Next, apply the starter fertilizer, being careful not to mix the two products directly in the spreader hopper, which can cause a chemical reaction and nutrient loss. Finally, spread the grass seed over the top of the lime and fertilizer.
Applying lime and fertilizer together can cause nitrogen loss as ammonia gas and may bind phosphorus, making it temporarily unavailable to seedling roots. These chemical interactions are minimized when using pelletized lime and starter fertilizer at recommended rates, but they confirm that simultaneous application is not the most efficient method.
The Optimal Staggered Application Schedule
When a significant pH correction is necessary, staggering the applications is the preferred, less risky alternative. Lime takes months to fully work, ensuring the soil environment is better suited to absorb the fertilizer’s nutrients before seeding.
The optimal strategy involves applying the required amount of lime first, especially if the soil pH is below 5.8, then waiting a period of two to four weeks before seeding. This delay allows some initial pH change to occur, ensuring the starter fertilizer applied with the seed will be more efficiently utilized by the new grass plants. If the soil test requires more than 50 pounds of lime per 1,000 square feet, the application should be split between two seasons to avoid shock and maximize the amendment’s effectiveness.