About NPKGuide

NPKGuide is a free fertilizer calculator and plant care reference. We built this tool because we could not find a modern, mobile-friendly resource that combined accurate NPK data with interactive calculators for home gardeners.

What is NPKGuide?

NPKGuide provides fertilizer dosage calculators, NPK recommendations, and seasonal schedules for 150+ plants. Every data point is sourced from university extension publications, not guesswork. The site is free to use, with no login required.

Our Data Methodology

We use a three-tier data quality system:

  • Tier 1: University-verified. NPK recommendations sourced directly from .edu extension publications with linked citations. This covers our top 50 plants and all lawn grasses.
  • Tier 2: Cross-referenced. Data compiled from multiple extension sources and verified for consistency. Used for 50+ additional plants.
  • Tier 3: General guidelines. Based on published horticultural reference books. Clearly labeled as general recommendations with a note to consult local extension services.

Every plant page shows its data source with a direct link. We update our database quarterly to incorporate new university publications.

University Sources

Our data comes from these university extension services:

  • Clemson University Cooperative Extension (HGIC)
  • Penn State Extension
  • Purdue University Extension
  • University of Georgia Extension (AESL)
  • University of Minnesota Extension
  • Oregon State University Extension
  • University of Illinois Extension
  • USDA Plant Hardiness Zone Map

Calculator Formulas

Our calculators use standard agricultural formulas. The dosage calculator uses this formula:

Pounds needed = (Desired N per 1,000 sqft / Fertilizer N%) x (Area / 1,000)

Burn risk thresholds are based on general extension guidelines: applications above 1 lb N per 1,000 sq ft are flagged as medium risk, above 1.5 lbs as high risk.

Disclaimer

NPKGuide provides general fertilizer guidance for educational purposes. Soil conditions, local climate, and specific plant varieties all affect fertilizer needs. Always follow your local university extension service recommendations for your specific conditions. When in doubt, get a soil test before fertilizing.

Product prices shown on this site are estimated and may not reflect current retail pricing. We do not sell fertilizer products.

Contact

Questions, corrections, or data source suggestions? Email us at [email protected] or visit our contact page.