Understanding those three letters on a fertilizer bag
You know those familiar N-P-K letters listed on a bag of fertilizer? The industry has standardized the nutrient listing on packaging with a three-digit system that tells you how much of these nutrients are in the bag. The listing is referred to as the three-digit ratio.
The N-P-K represents the three main ingredients found in fertilizers: N stands for nitrogen, P for phosphorus, and K for potassium. Along with each letter is a number. These letters, N-P-K, never change, but the numbers associated with each letter does. The choice of ratio can vary for your particular need.
The general garden rule of thumb when remembering what part of the plant each letter benefits, so you know what you want to target, is:
up and down and all around
Here’s good way to remember what each letter focuses on:
UP: N stands for nitrogen and its primary function is for the green part of the plant; the upper part of the plant.
DOWN: P stands for phosphorus and it’s primary function is for the roots of the plant.
ALL AROUND: K stands for potassium and its primary function is for the overall health of the plant.
As such, the garden rule of thumb to remember N-P-K is three key nutrients helping the plant up and down and all around.
Too much N will produce nothing but green leaves. Too much phosphorus and you plant will have a strong room system, but little green on top. Too much K and your plant will have trouble taking on other nutrients. 10-10-10 is a general balanced fertilizer.