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On this page, I’ll answer your questions and provide some nuggets of wisdom on anything related to slow release fertilizers…

Thursday, May 20, 2010
How to Read A Fertilizer Label

Here’s How: (credit to the amazing guide over at – Remember also to read all the great content on – this is such a critical topic!
Major Ingredients: Most commercial fertilizers have 3 numbers on the front label, separated by dashes. For example: 5-10-5. This is the fertilizer analysis or percentage by weight of the 3 major nutrients plants need: nitrogen, phosphorus and potassium, in that order. These are abbreviated as N-P-K.So if you purchased a 10 pound bag of fertilizer labeled 5-10-5, it would contain 5% nitrogen, 10% phosphorus and 5% potassium. The remaining 80% could be comprised of other nutrients and filler.

1st Number = Nitrogen: The first number gives the concentration of nitrogen in the product. Nitrogen encourages foliage growth, among other benefits. A 5-10-5 fertilizer would contain 5% nitrogen by weight. So for every pound of fertilizer applied there is really only .05 pounds of nitrogen. (The 10 pound bag mentioned above would contain .5 lb. nitrogen.)

2nd Number = Phosphorous: The middle number refers to the concentration of phosphorous. Phosphorous contributes to many fundamental plant processes such as rooting and setting flower buds. A 5-10-5 fertilizer would contain 10% phosphorous by weight or .1 pounds of phosphorous. (The 10 pound bag mentioned above would contain 1 lb. of phosphorus.)

3rd Number = Potassium: The final number states the concentration of potassium. Potassium contributes to the overall health and vigor of plants. Again, a 5-10-5 fertilizer would contain 5% potassium by weight or .05 pounds of potassium. (The 10 pound bag mentioned above would contain .5 lb. potassium.)

Complete Fertilizers: Fertilizers that contain all three major nutrients are considered complete fertilizers. There are specialized fertilizers which are called incomplete because they lack one or more major nutrients such as a fertilizer labeled 0-20-20.

Fertilizer Ratio (An easier comparison): An easier way to compare the numbers is to break them down to the fertilizer ratio or the amounts of the 3 major nutrients in relation to each other. A 5-10-5 fertilizer has a ratio of 1-2-1. This becomes important when looking for a fertilizer for a specific need. A 1-2-1 ratio is often recommended for vegetables, which need plenty of phosphorous to set fruit. 1-2-1 could be 5-10-5, 10-20-10 or any similar extrapolation.

Other Ingredients: Any additional ingredients will be listed on the side label. This may include other nutrients like calcium, magnesium, iron, micronutrients and even the percentage of organic matter.

Organic fertilizers: Organic fertilizers must specify which nutrient(s) is organic and it must be identified as either synthetic and/or natural, by percentage. For example: 20% of Nitrogen organic (6% synthetic, 14% organic). When a fertilizer is labeled “organic”, it simply means it contain carbon atoms. It can be naturally produced from plant or animal tissue or synthetically manufactured.7:20 pm edt 

Summer is almost here, beware quick release…Friends, with summer upon us, and temperatures starting to get into the 80’s and 90’s in some parts, its important to realize that fertilizer can be your friend or foe.  In the hot hot summer, quick release fertilizers can burn the plant’s roots and also foul our precious water supply.  Be smart, be aware, and think slow release….3:32 pm edt