There are three numbers on a fertilizer label, such as 8-8-8, 10-10-10, or 10-20-10, that are important to understand what each number means before purchasing or using the fertilizer. Of course, knowing what these three numbers mean is not enough to make a good decision about fertilizer use. You need to understand why each of the three nutrients is important.
Before I delve into demystifying fertilizer labels by explaining the meaning behind each number, lLet me briefly examine the three primary macronutrients plants need to stay healthy: nitrogen (N), phosphorus (P), and potassium (K).
Note that there are also micronutrient requirements, which is why it’s important to have your soil tested every few years. The results of the soil analysis provide information about the availability of nutrients in the soil, whether there are nutrient deficiencies and the necessary corrective measures. Contact your local district extension office for more information and where to submit soil samples for analysis.
Nitrogen is an essential nutrient for plant growth and an essential part of every plant cell. When nitrogen is sufficient, plants synthesize more protein and promote cell division and cell growth, which means the leaf area of plants increases rapidly and more leaf area is available for photosynthesis.
Nitrogen stimulates rapid growth of branches and leaves, causing leaves to be greener and grow faster. In general, during the growth phase of foliage and flowering plants, nitrogen encourages the development of new branches and thickens the leaves.
Adding a 3- to 4-inch layer of mulch such as grass clippings, pine bark, pine straw, hay, or leaves that will decompose over time are excellent sources of organic nitrogen.
The key role of phosphorus is to support plant root development, grow more branches in green plants, and distinguish flower buds more quickly in flowering plants. After the branches and leaves grow luxuriantly, the plants enter the reproductive phase. The application of fertilizers with increased phosphorus levels can promote the differentiation of flower buds, flowering and fruiting.
Fish emulsion, composted chicken and cattle manure, bone meal, and powdered egg shells are often good organic phosphate fertilizers.
During plant growth and development, potassium activates numerous enzyme systems, photosynthesis, carbohydrate uptake and protein synthesis. Potassium is the basic building structure that allows plants to grow stronger and enhances the plant’s ability to resist disease.
When used in combination with phosphorus, it promotes robust growth, flowering and fruiting. Commonly used organic potassium fertilizers are plant ash, which is produced from burning garden waste such as branches, other plant materials, or from banana peels.
What do the numbers on the fertilizer labels mean? Fertilizer numbers indicate the NPK ratio: N is nitrogen, P is phosphorus, and K is potassium. The numbers represent the weight percent of a nutrient in the fertilizer. For example, “10-20-10” fertilizer contains 10% nitrogen, 20% phosphorus, and 10% potassium.
Remember that nitrogen, phosphorus, and potassium aren’t the only nutrients plants need to survive and grow. Of all the nutrients they need, plants use more NPK (I call them “the big three”) than any other nutrient.
So, gardeners, let’s get out there and build a greener, more sustainable world, one plant at a time!
If you have specific gardening questions or want more Contact the Orange County Master Gardeners for more information Helpline: (409) 882-7010 or visit our website: https://txmg.org/orange, Facebook: Orange County Texas Master Gardeners Association or E-mail: [email protected].
