Maintaining a healthy lawn often requires supplementing the soil with commercial fertilizers. These products are labeled with a three-number code, such as 13-13-13, which indicates the percentage of three primary nutrients. Choosing the correct formulation is important for ensuring the grass receives the necessary elements without causing nutrient imbalance. The suitability of a balanced fertilizer like 13-13-13 depends entirely on the specific stage and needs of the turf.
Understanding the NPK Ratio
Fertilizer labels use the NPK ratio to communicate the proportion of nitrogen (N), phosphorus (P), and potassium (K) contained within the bag by weight. A 13-13-13 formulation contains 13% of each of these three macronutrients, which fulfill distinct biological functions required for plant growth.
Nitrogen promotes lush, green, above-ground growth by aiding in the production of chlorophyll. Phosphorus supports strong root development and energy transfer, making it important during the establishment phase. Potassium strengthens the grass against environmental stressors like drought and disease.
When 13-13-13 is Ideal for Lawns
A balanced blend like 13-13-13 is most appropriate when establishing new turf from seed or laying down sod. This formulation functions as a “starter” fertilizer, providing the necessary supply of phosphorus for new root systems. Young seedlings require significant phosphorus to develop deep, anchoring roots for long-term stability. The equal inclusion of nitrogen ensures initial green-up and rapid leaf development begins without delay.
The balanced ratio is also suitable if a soil test confirms a general deficiency across all three macronutrients. Soil testing is the most accurate way to determine if the lawn is lacking in phosphorus and potassium alongside nitrogen. Applying 13-13-13 to correct a verified deficiency ensures that all three primary nutrients are replenished simultaneously.
Why Established Lawns Require Different Nutrient Levels
For the ongoing maintenance of a healthy, established lawn, a 13-13-13 blend is not the best choice. Established turfgrass requires significantly more nitrogen to maintain color and density than it does phosphorus or potassium. Maintenance fertilizers typically feature a much higher nitrogen percentage, often following ratios such as 4-1-2 or 3-1-2, resulting in products like 20-5-10 or 16-4-8.
Repeatedly applying a balanced fertilizer like 13-13-13 on established grass can lead to an accumulation of unnecessary phosphorus and potassium in the soil. This nutrient buildup can interfere with the absorption of other micronutrients. Excess phosphorus is a concern because it contributes to water runoff issues and impacts local water quality. Therefore, maintenance programs focus on high-nitrogen applications, adjusting other nutrients only as indicated by testing.
Safe and Effective Application
When a soil test or new turf establishment calls for a balanced fertilizer, careful application techniques must be used. Fertilizer granules should be distributed evenly across the lawn using a calibrated broadcast or drop spreader. This ensures consistent coverage and prevents streaks of over- or under-fertilized grass. The general application rate for a 13-13-13 product is often around 4 pounds per 1,000 square feet, delivering approximately 0.5 pounds of actual nitrogen.
Apply the fertilizer to dry grass to prevent the granules from sticking to the blades, which can cause chemical burn. Immediately after spreading, the area must be lightly watered to wash the fertilizer off the grass blades and move the nutrients into the soil. Watering prevents burn and initiates the nutrient breakdown process, making the elements available for root uptake. Always sweep any granules off paved surfaces like driveways or sidewalks before watering to prevent nutrient runoff.