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What Do Fertilizer Numbers Mean?

Anyone that has used fertilizer products has probably noticed the fertilizer numbers that prominently present on sides of the products’ containers. In most cases, they show up on the front, but are also commonly located near the bottom of the container’s back or on the side. These fertilizer numbers are used to impart valuable consumer information by providing a breakdown analysis of the fertilizer’s nutrient/chemical contents. However, not everyone understands exactly how to read them or what they signify.

Generally speaking, the numbers refer to the parentages of Nitrogen, Phosphorus and Potassium, by weight, listed in this exact order and contained in the fertilizer. These numbers stand for the percentages contained within a specific package. For instance, an all-purpose garden fertilizer is typically referred to as 10-10-10, meaning that equal portions of the aforementioned nutrients are contained in the fertilizer mixture. Someone that purchased a bag of this mixture weighing 50 pounds, five pounds of the mixture would be Nitrogen; another five pounds would be Phosphorus and another, Potassium. Fillers are used for the remaining 70% to help disperse the nutrients or chemicals.

What Do Fertilizer Numbers MeanEach chemical used in fertilizer mixes has a specific purpose. With its ability to impart plants with the ability to produce additional chlorophyll, Nitrogen is added to help promote above ground plant growth. This includes green leafy foliage and lush lawn grass. If one is seeking a fertilizer to help with these issues, he or she should look for a fertilizer with a higher first number that indicates that more Nitrogen is being used in the mixture. A Nitrogen-rich fertilizer can help plants grow taller and more quickly. It also helps green plants develop a darker, greener color. When used on lawns, a Nitrogen-rich fertilizer will make the grass grow faster, so the additional maintenance should be a consideration before infusing a lawn with a fertilizer that has a higher Nitrogen content.

The middle number indicates the percentage of Phosphorus that is being used. Phosphorus is generally used to establish or promote below ground growth. It is also used to support fruit production and blooming flowers. The gardener who is looking for a fertilizer to result in heartier flower blooms or that is seeking a starter fertilizer for his or her lawn should look for one that has a higher middle number. Gardeners that grow roses and other flowers to enter into competitions will often choose to use a fertilizer rich in Phosphorus because it helps the blooms to be larger and richer in color. Phosphorus can help foster the development of new plants such as trees, shrubs and other plants that are just starting out in a lawn or garden.

Potassium is an important element used in promoting overall plant health. It works by helping plants build stronger cells within their tissue. Potassium helps plants withstand heat better. Plants with added Potassium also tolerate cold, insects, diseases and other stressors better. When shopping for a fertilizer for winterization of one’s garden, it is important to select one that has a higher third number.

A good way to tell which combination of nutrients/chemicals will work best in a lawn or garden is to note the coloring of the stems, leaves and flowers of the plants. For instance, if plants begin to turn yellow or light green, this may be a call for more Nitrogen. If a plant that is normally green begins to turn purple or shows purple streaks throughout it, it is most likely that this plant needs a fertilizer with a higher middle fertilizer numbers, signifying a higher Phosphorus content. While this signs are indicative of a nutrient deficiency, the best way to make a more exact determination about which fertilizer to buy is to perform a soil test.

Soil tests can be obtained through virtually any state’s Cooperative Extensive Service for a nominal fee. Many services offer them free of charge. The soil test can not only determine which nutrient or chemical is needed. It can also help determine the amounts of fertilizer that are needed. Once a gardener understands what fertilizer numbers mean, his or her gardening tasks become much less mysterious and much more productive. Using the right combinations of Phosphorus, Nitrogen and Potassium can make all the difference in the success of one’s plant growing endeavors.

About the author

Mark Kelly

Hi, I'm Mark the owner of Yard Care Gurus. I love to be outside working on my lawn, planning my next project. I created this website to help people like you find the best products for yard care and great advice. Thanks for stopping by!

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