Getting Started

How Do You Make Sense of Numbers on Fertilizer Bags?

shutterstock_411632566Fertilizing your garden may take more than just a quick trip to the store to pick up a bag of mulch. This is because fertilizer intends to supplement the nutrients a plant needs, and the needs may vary from plant to plant. When it comes to fertilizers, it will definitely never be a one-size-fits-all kind of deal.

To help you determine what each fertilizer is meant for, a code is conveniently indicated up front in three big numbers. Go and check out a bag of fertilizer. It will always be indicated on the label.

These three big numbers signify the percentages of Nitrogen, Phosphorous, and Potassium in the fertilizer you are buying. This is otherwise known as the NPK%.

Why N-P-K?

Just as sugar, and spice, and everything nice makes a perfect little girl, N-P-K makes a healthy plant. These three are the main macronutrients that plants need in order to grow healthily. However, they are often lacking in the soil. This is why we turn to fertilizers for help.

Nitrogen promotes top growth and the production of strong, abundant foliage. That means all things green and leafy need to eat up a lot of nitrogen to get by. It works by promoting the production of chlorophyll. This not only means that your plant will look greener, but that it will have a better capability of producing its own food through photosynthesis.

If your leaves are looking fairly yellow, then that is a clear sign that your plant is suffering from nitrogen deficiency. Nitrogen is the scarcest of these three macronutrients. You can definitely add more nitrogen to the mix in the form of blood meal, or by adding coffee grounds into your compost.

But be careful. Adding nitrogen may be easy, but the effects of excessive nitrogen may be adverse and much trickier to reverse. Too much nitrogen takes away moisture from the plant and leaves behind mineral salts in the soil. This may stunt root growth and flowering. If the plant absorbs too much nitrogen, it would tend to focus all its power on producing more foliage and not enough flowers or fruit.

Phosphorous, however, can take care of that problem.

Phosphorous promotes flowering and fruiting. This chemical also helps the growth of strong roots. It improves overall vitality and promotes seed growth. Phosphorous works mainly in activating the enzymes that allow the plant to transfer energy through its system. Typically, flowering plants may need more phosphorous than a leafy plant like a potted herb.

Potassium, on the other hand, is a nutrient that is present and absolutely necessary in every part of the plant. It helps regulate the uptake of Carbon Dioxide during photosynthesis. Potassium also triggers enzymes for the production of energy sources.

In addition, it promotes the uptake of water of plants through the roots and regulates water loss through the stomata. Because of this, Potassium is a key ingredient in improving a plant’s capabilities to survive through drought. 

Plants just simply cannot grow without any source of potassium because it’s the macronutrient that activates all the necessary enzymes for growth and protein production.

NPK % versus NPK Ratio

The numbers on the fertilizer label show the percentages of a specific macronutrient in the fertilizer itself. If, for example, your fertilizer says 12-12-12, that means for every 100 grams of fertilizer, there is 12% Nitrogen, 12% Phosphorous, 12% Potassium. The rest of the 64% is inert material. This just means it is inactive ingredient or filler soil, and does not intend to provide the plant with nutrients.

But when it comes to NPK Ratios, a 12-12-12 fertilizer and a 5-5-5 fertilizer are the same ratio. They are all 1:1:1. Similarly, a fertilizer labeled 24-8-16 and one labeled 9-3-6 are both following a 3:1:2 ratio.

Both of these ratios are examples of fairly typical fertilizers that are meant for general usage. They address the needs of most garden plants.

Despite having the same NPK Ratio, an organic fertilizer may be labeled with lower NPK% because by regulation.

Fertilizers must also be labeled according to the readily present nutrients. With organic fertilizers, typically the case is that they are slow releasing, which explains for the low initial NPK%.

Fertilizers that supply N, P, and K are called complete fertilizers. Fish emulsion is a good example of organic complete fertilizer, with NPK of 5-2-2. However, some fertilizers may also aim only to provide one or two of these macronutrients.

Bone meal is a common Phosphorous-focused fertilizer, with an NPK% of 1-13-0. Inversely, Blood Meal focuses on Nitrogen and has an NPK% of 13-1-0.

How much of N-P-K do I need?

When it comes to the formula of fertilizer you need, it will always come down to what kind of plants you intend to grow and for what. You can always start off with a fertilizer with a 1:1:1 NPK Ratio. If your soil is less acidic or you notice your plants may need more Nitrogen, opt for a 3:1:2 generic fertilizer. Sunflowers and snapdragons both enjoy fertilizers of the 3:1:2 variety.

If you are growing leafier foliage, choose fertilizers labeled with higher Nitrogen content. And if you are growing flowering and fruiting plants, aim for a Phosphorous rich fertilizer.

You can also use fertilizers on a schedule. 16-6-4 is a good choice for the spring time, when foliage is only about to grow. On the other hand, 3-20-20 would be better used towards the end to promote fruiting and flowering for the harvest season. This kind of fertilizer also stimulates root growth and stem vigor.

If your soil already has the right amount of nutrients but lacking in one, opt for an incomplete fertilizer that targets the specific needs. It’s better to do this rather than use another complete fertilizer and create an excess of a certain nutrient. Typically, Nitrogen is scarcer in soil, so go for a Nitrogen rich incomplete fertilizer instead.

Overdosing the soil with phosphorous can also be detrimental to flowering plants. Certain flowering trees, most notably the South African Sugarbush, have been known to binge on excess phosphorous and die from it.

Needs Plus Knowledge

When you know specifically what it is that your garden needs, and you have the knowledge on how to best supplement those needs, your garden will certainly grow. Always read up on the targeted plant care specifications of the plants you are growing. Assess the pH of your soil and the water levels. These too will affect how your plants absorb the soil.

If you do all these, and you pick the right fertilizer for your luscious green friends, there will be no limits to what your garden can achieve.

Happy Gardening!


Click to comment

Leave a Reply

Your email address will not be published. Required fields are marked *

Most Popular

To Top