Reference
What Do the NPK Numbers on Fertilizer Mean?
The short answer
The three numbers on a fertilizer bag (like 10-10-10) are the percentages by weight of nitrogen (N), phosphorus (P), and potassium (K), always in that order. Nitrogen drives leafy green growth, phosphorus supports roots, flowers, and fruit, and potassium keeps the whole plant vigorous and stress-tolerant.
So a 'balanced' fertilizer like 10-10-10 has equal parts of each; a high-first-number product (e.g. 24-0-6) is mostly nitrogen for leafy growth or lawns. Match the ratio to the job — but test your soil before loading up on phosphorus, since many garden soils already have plenty.
What each number does
- N (nitrogen) — leaf and stem growth, deep green color. Leafy crops and lawns want more.
- P (phosphorus) — root establishment, flowering, and fruiting. Many soils already have enough; a soil test tells you.
- K (potassium) — overall vigor, disease and stress tolerance.
How to read a label
A number like 5-10-10 means 5% N, 10% P (as phosphate), 10% K (as potash) by weight; the rest is filler and carrier. Higher numbers = more concentrated, so you apply less. 'Balanced' means the three numbers are equal.
✔ Don't assume more phosphorus = more flowers. Extra P doesn't help if your soil already has enough — a soil test prevents waste and runoff. For a specific plant's rate and timing, use GardenSays' fertilizer tools.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Minnesota Extension — Quick guide to fertilizing plants — Fertilizer labels list N-P-K as percentages of nitrogen, phosphorus, and potassium in that order; match the analysis to the plant's needs and a soil test.
- The Old Farmer's Almanac — N-P-K Ratio: What Do the Numbers Mean — The three fertilizer numbers are the percentages of nitrogen (leaf growth), phosphorus (roots/flowers/fruit), and potassium (overall health), in that order.