The Fertilizer Grade

— Written By and last updated by Tamara Carawan
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bag of fertilizer

Fertilizer is often one of the most overused and underused products in the home landscape. It is easy to get overwhelmed when purchasing fertilizer, as numerous products are available in various grades (10-10-10, 8-0-24, 32-0-10, etc.) and are marketed with language like water-soluble, slow-release, and special crop specific blends. However, with a little knowledge, we can quickly strip away the mystery of fertilizer and make better choices that will benefit our landscapes.

There are 16 essential elements that plants require for growth. These 16 elements can be broken down into three categories: primary macronutrients (required by plants in largest quantities), secondary nutrients, and micro or trace nutrients. Available fertilizer products typically supply some portion of the macronutrient’s nitrogen, phosphorus, and potassium. These nutrients are represented by three numbers on the label, either containing all three elements in a complete form (8-8-8), or an incomplete form containing only one or two of these elements (15-0-15, 21-0-0). Some fertilizer products will also contain secondary and micronutrients along with these macronutrients. Just like a food nutrition label on your favorite snack food, each fertilizer product contains an analysis section on its label that specifies what percentage of nutrients are within that product. Products that contain a larger percentage of a given nutrient contain more pounds of that nutrient per pound of product. This means it will take less of a larger percentage product to cover a given area than a lower percentage product. With this information, we can calculate how much nitrogen, phosphorus, and potassium each product supplies, determine how much product is required to fertilizer a given area, and compare the cost of various fertilizers.

You will also notice that many of these fertilizer products are derived from similar sources such as urea, potassium chloride, ammonium phosphate, etc. It is the combination of these sources that determines what final grade or analysis the fertilizer product contains. You might also see on the label information like polymer or sulfur coated urea. This represents a portion of the nitrogen within that product that has been treated with a coating that slowly wears away, resulting in the slow-release claim on the label. Water-soluble fertilizers are products that will dissolve completely in water with some nutrients that can be immediately utilized by plants. These water-soluble products can be beneficial for plants that are showing signs of nutrient deficiencies (yellowing, leaf chlorosis).

Fertilizer nutrients can come from naturally occurring source materials or from refined sources that produce a more stable or soluble product with greater concentrations of nutrients. Once applied to soil, chemical and biological processes make available these nutrients to plants. Regardless of packaging claims, plants do not care where the fertilizer was sourced from, but only that enough nutrients are available to perform cellular functions.

To determine how much fertilizer your lawn and garden may require, homeowners are encouraged to start their fertilization program with a soil test through the North Carolina Department of Agriculture and Consumer Services Soil Testing Lab. From this test, you will receive a recommendation for lime and fertilizer specific to your crop. Although lime is not generally considered a fertilizer, it can benefit acidic soils by raising soil pH levels to recommended crop ranges. This allows greater nutrient availability to plants and improves overall growth. Please be aware that homeowners should never routinely lime their soils without the recommendation of a soil test. This can create poor growing conditions that are not easily corrected.

If you have questions about fertilizer, soil testing, or additional questions related to fertilization, please contact Daniel Simpson at 252-745-4121 or