What do the three numbers mean on fertilizer bags?

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Have you ever wondered what that three-digit number on the front of fertilizer bags means? It represents the three main fertilizer nutrients (nitrogen: N, phosphorus: P and potassium: K). They are always listed in the same order to make up a three-digit formula: N-P-K. Each of these three nutrients is designated by a number — a percentage of the pounds of each per hundred pounds of fertilizer. For example, a 20-10-5 formulation means there are 20 lbs. of nitrogen per hundred pounds of fertilizer, 10 lbs. of phosphoric acid and 5 lbs. of potassium. When you select a fertilizer, remember the purpose of each ingredient and relate the percentages to the needs of your plants and/or lawn. Choose fertilizer with the highest first number for fast-growing grass. Choose fertilizer with the highest middle number for good flower and vegetable production. Choose fertilizer with the highest last number to toughen your plants against disease and winter′s cold.