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NPK: The Golden Ratio of Plants
Nitrogen, phosphorus and potassium are essential parts of your plant's diet.
Every container or bottle of plant food has a set of three numbers written on the label like this: 12-4-8. It's not a cryptic message—it's just the NPK ratio, sometimes just called NPK or the guaranteed analysis, and it's important to understanding how plant food helps your plants.
What does NPK Stand For?
NPK or N-P-K stands for Nitrogen (N), Phosphorus (P) and Potassium (K). These three elements make up the three primary macronutrients, or the nutrients your plant needs in the largest quantities. All plant food or fertilizer products, from Miracle-Gro® or other brands, must have an NPK ratio on the label. You'll also see an NPK ratio on lawn fertilizers. It's our guarantee to you how much of these three macronutrients will be in the product—hence the name "guaranteed analysis."
The numbers tell you the percent of each nutrient that's present in your plant food and give you the proportions of each nutrient. For instance, 12-4-8 means the plant food has 12% nitrogen, 4% phosphorus and 8% potassium. The ratio proportion can be reduced to 3-1-2, or three parts nitrogen to one part phosphorus to two parts potassium.
This ratio varies from plant food to plant food. Some plant foods may not contain one or more of these macronutrients (represented by a "0" in the ratio). Complete plant foods have all three primary macronutrients, and balanced plant foods have an equal ratio (for instance, 20-20-20).
As part of the expanded analysis on your plant food label, you may also see secondary macronutrients and micronutrients with the percentages listed. While your plants benefit from these nutrients as well, they're needed in smaller quantities. The secondary macronutrients are calcium (Ca), magnesium (Mg) and sulfur (S). There are nine micronutrients, including iron (Fe), copper (Cu) and boron (B).
How Nitrogen, Potassium and Phosphorus Help Plants Thrive
Let's take a closer look at the primary macronutrients and what they do for plants.
Nitrogen: The Green Machine
Nitrogen makes plants green and helps them grow. From photosynthesis to building cell walls, nitrogen is involved in a lot of your plant's growth processes. It's a component of chlorophyll, the chemical that makes your plants green and helps them harvest light from the sun to convert into energy. Amino acids, the building blocks of protein formation, also contain nitrogen. Proteins do a lot for your plants, including helping build cell walls and enzymes. Nitrogen is also found in nucleic acids such as DNA.
Plants with nitrogen deficiency may have yellow leaves, especially the oldest leaves. You may also notice that your plant's growth has slowed. As nitrogen deficiency continues, more parts of the plant become affected, including yellowing new leaves, smaller or thinner shoots, or even smaller and reduced numbers of flowers or fruit.
Phosphorus: Your Plant's Power House
Phosphorus is key for energy production, which your plant uses for root growth and flower, fruit and seed development. It's a component in the molecules that store and release energy in your plants, and it can be found in DNA and RNA. Plants lacking phosphorus may have darker-than-usual leaves, or even blue-green or purple leaves. Growth may appear stunted with shorter stems, smaller leaves or fewer flowers. Leaves may also drop prematurely or curl and become distorted. Underneath the soil, weaker root systems may make your plant more susceptible to water stress.
Potassium: Stress Relief for Plants
Your plants need to develop resilience to survive stressors like drought, frost, insects and diseases. Enter potassium, which is involved in processes like photosynthesis, protein synthesis, moving water and nutrients inside the plant, building strong cell walls, cell expansion and opening and closing pores that let carbon dioxide in and oxygen out (essentially plant "breathing"). If that sounds like a lot, it is! When these processes are healthy, it adds up to a plant that's better able to combat stresses. Many of the symptoms of potassium deficiency are similar to nitrogen and phosphorus deficiencies, including water stress, yellowing, bluish-green or curling leaves, and stunted growth. Plants with a potassium deficiency may also develop leaves with yellowing or browning edges.
What ratio is right for your plants?
Typically, a 3-1-2 ratio is considered ideal for most plants, like the 12-4-8 ratio found in Miracle-Gro® Shake ‘n Feed® All Purpose Plant Food, but this can vary based on the type of plant or its stage of growth. For instance, young transplants benefit from a boost in phosphorus to improve root growth, making the 4-12-4 ratio of Miracle-Gro® Quick Start Planting and Transplant Starting Solution a great choice. Flowering plants also need phosphorus to promote more blooms and benefit from feedings with Miracle-Gro® Water Soluble Bloom Booster® Plant Food (15-30-15).
With Miracle-Gro® plant foods, you don't have to guess what your plants need. We have a variety of plant foods to help specific plants grow healthy and strong throughout their lifecycle. With granular, water soluble and liquid plant food options, you can find a solution that works for you.
