Phosphorus (P)
The middle number in an NPK ratio. Phosphorus supports root development, seed germination, and early establishment. Established lawns often need little or no phosphorus — many modern fertilizers list 0 for the middle number.
Phosphorus (P) is critical for new lawns, overseeding, and root establishment. "Starter fertilizers" are high in phosphorus for this reason. However, established lawns with healthy soil typically have adequate phosphorus and adding more can lead to runoff and water quality issues.
Many states restrict or ban high-phosphorus fertilizers for established lawns due to environmental concerns about phosphorus runoff into lakes and waterways.
Soil test: The only reliable way to know if your lawn needs phosphorus is a soil test. If your soil already has sufficient phosphorus, adding more provides no benefit.
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