Fertilizer contains nutrients that plants need to thrive. The three main nutrients being nitrogen (N), phosphorus (P) and potassium (K). The numbers on fertilizer stand for the proportion of those nutrients contained in the product.
Fertilizers, no matter the brand, will always show the nutrient proportions in the same order separated by hyphens: first nitrogen, then phosphorus, then potassium.
Balanced vs. Imbalanced
Fertilizers that list numbers close to one another in value are considered balanced. To be balanced, no number can be more than twice another number. Thus, a 10-15-10 fertilizer is balanced.
When fertilizer has more of one element than the others, it's often referred to as if it contains only that element, though it still contains all three. Thus, a 15-5-5 fertilizer might be called a nitrogen fertilizer.
The reason fertilizers include nitrogen is that the element isn't a natural component of soil. Phosphorus and potassium are but can be difficult for roots to find.
What the Nutrients Do
Nitrogen helps new leaves develop, phosphorus is important for flowering and helps roots, while potassium is especially helpful to fruit development.
- A Garden of Your Own; Michael O'Brien; 1993
- A Homeowner's Guide to Fertilizer
- Alabama Cooperative Extension-Hydroponics
- Utah State University Cooperative Extension
fertilizer numbers, fertilizer percentages, fertilizer proportions
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