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What do the numbers on the fertilizer package mean?

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A

N-P-K.  The first number (N) is nitrogen is an important element for leaf growth, color and development.  Phosphorus (P) is used by the plant for root development and seed production.  Potassium (K) is used by the plant for disease resistance, hardiness and sugars.  Sometimes a fourth number may follow the third, indicating presence of another element like sulphur, iron or zinc.  Federal and State laws require all fertilizer labels to represent the actual percentage of nitrogen, phosphorous, and potassium by weight.  Thus, ammonium sulfate (21-0-0) contains 21% nitrogen by weight and provides neither P nor K.

Posted on 13 Jun 2006

Karl Hauptfleisch
Salt Lake Master Gardener

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