What Do Fertilizer Numbers Mean?
Published 2026-10-27
Every bag of fertilizer shows three numbers, like 10-10-10 or 13-0-0. Those numbers are the guaranteed analysis of the three main plant nutrients, and understanding them makes it much easier to choose the right product for your lawn, flowers, vegetables or shrubs. This guide decodes the numbers and explains when to use balanced, high-nitrogen and high-phosphorus fertilizers.
N-P-K: what the three numbers are
The three numbers are always in the same order: nitrogen (N), phosphorus (as phosphate, P) and potassium (as potash, K). Each number is the percentage of the bag's weight. A 10-pound bag of 10-10-10 contains about 1 pound each of nitrogen, phosphate and potash; the rest is filler and other materials that help spread the nutrients evenly.
What each nutrient does
Nitrogen supports leafy green growth, which is why lawn foods and blood meal are high in nitrogen. Phosphorus supports root development, flowering and fruiting, which is why bone meal is popular at planting time. Potassium supports overall plant health and resistance to stress. A soil test from your local extension service shows which nutrients your soil actually lacks.
Balanced vs specialty fertilizers
Balanced fertilizers like 10-10-10 and 13-13-13 have equal amounts of each nutrient and are a simple all-purpose choice for many gardens. Blood meal (13-0-0) adds nitrogen only, while bone meal (3-15-0) adds mostly phosphorus. Specialty blends for citrus, evergreens or flowers adjust the ratio for those plants. Pick based on what you are growing and what your soil needs.
Apply safely and effectively
Always follow the application rate on the label; more fertilizer is not better and can burn plants or wash into waterways. Water granular fertilizers in after applying unless the label says otherwise. Keep fertilizer away from children and pets, store bags sealed and dry, and sweep any granules off sidewalks and driveways back onto the soil. Feeding plants during their active growing season, rather than when they are dormant, gives the best results. Wear gloves when handling fertilizer and wash your hands afterward.
