Understanding Fertilizer Numbers and Letters

spraying Fertilizer

Lawn Fertilizers (N-P-K Ratings Explained)

Have you ever wondered how that annoying neighbor, (you know, the one with the picture perfect house & yard), manages to get such a brilliant green hue to his lawn?

You know the one that stands out from the rest of the neighborhoods yards with no clover or dandelions, against the ones that have a little yellow showing, maybe some brown patches. What’s he doing so different than the rest of us?

I’d say it’s a safe bet that “Mr Green” has learned that there is really only two things you need – copious quantities of two essentials – fertilizer and water.

He’s undoubtedly broadcasting liberal amounts of a granular fertilizer, or perhaps is a fan of a concentrated liquid lawn fertilizer. With either method the results will be the same – a lush, healthy & green lawn.

The Two Types of Fertilizer

The water is pretty self-explanatory, but what about fertilizer? If you’ve ever spent time in your local greenhouse big box store, you’ve likely been a little bewildered by all the varieties available. It can be quite bewildering as they’re all marketed differently; a Pet safe lawn fertilizer, natural organic lawn fertilizers, winter lawn fertilizer to name, Vigoro lawn fertilizer just a few. Common to all though will be the N-P-K rating. Just what do all those numbers on the bags mean?

Let’s simplify it. There are basically two types of fertilizers;

The Organic Type – Found in rotting plant matter, (compost is a good example) etc, and in animal manure. Often a homemade lawn fertilizer, these types are truly natural organic lawn fertilizers

Manufactured Fertilizer – Made by lawn fertilizer companies, this is the type you’ll see in stores. Often in a granular form, sometimes as liquid lawn fertilizers, they will both be labelled with three numbers, e.g 11-51-0

Let’s explain the mystery of the basic elements of manufactured fertilizer, what those 3 numbers actually mean, and what you should be looking for when making a purchase of fertilizer

Understanding the basics will have you giving “Mr Green” a bit of a challenge in no time.


The Macro Elements

First the numbers, the “N – P – K”

There are three basic elements of all fertilizers (the macro elements) and it doesn’t matter whether you’re using a manufactured fertilizer or an organic type – it’s the nutrients that count, as each element is absolutely necessary for all plant life to grow. Of course water and sunlight are necessary, but without being fed the right nutrients you’ll have a sad looking plant, especially if you’re trying to grow Zoysia Grass.

These nutrients are commonly called the N-P-K analysis of the fertilizer, and they are always shown in the same order. Each element is the foundation, or building block, of the growth of plants and every element is essential.

So what does each letter stand for and what does each element do?

  • N is for Nitrogen
  • P is for Phosphorous
  • K is for Potassium

Let’s look at each element in turn, and see why it’s important you understand each function.

Further Reading: Check out which Lawn Sweeper is the best here!

N – Nitrogen

Always the first of the three numbers (NPK).

Essential for both growth and color, the macronutrient Nitrogen (N) is used by all plant life, but plants such as grasses (the majority of your lawn is different grass species) are voracious users of nitrogen, and lawns will require ample amounts of it throughout the growing season. Packaged fertilizers generally contain two distinctly different forms of this element.

Nitrate Form – Quite often you’ll see this called a “Quick Release” fertilizer as it’s main attribute is it’s ability to be rapidly absorbed by growing plants, meaning you’ll experience a visual change in your lawn almost immediately for instant gratification! This attribute can also mean that it can be equally leached from the soil profile. Periods of heavy rainfall can wash this form from the soil quite rapidly.

Ammonium Form – the “slow release” form of Nitrogen. This form of N bonds to the soil particles on application, and it quite stable and lasts considerably longer than the nitrate form. Because of this stability, this N form takes a lot longer to move into the plant through the root system, resulting to a more prolonged feeding period.

To keep a lawn healthy, green & lush throughout the whole season you actually need both forms of N. Though you can certainly make separate application of each I much prefer to broadcast a mixture, or blend, or each.

By doing so the quick release Nitrate form will deliver an immediate boost, then as it peters out the Ammonium form kicks in with a more gradual release.

In short, don’t get too stuck on the numbers, just make sure you have some of both in the fertilizer you buy.

Understanding the numbers

It’s really pretty basic – the higher the number the more of that element in the fertilizer analysis. A widely used N form used by farmers for example is 46-0-0, meaning that pure Nitrogen is 46% of the weight of the fertilizer.

So if you have a tonne (1,000 kgs) of the actual product, then 460 kgs would be actual Nitrogen. Farmers will analyze their soil & the results will often call for a specific amount of “actual N” per hectare, so it becomes pretty simple to ascertain how much of the actual fertilizer to apply.

Understand the numbers and you too can make these calculations with ease!

Understanding the basics

All you really need to remember, that for the average homeowner to enjoy a healthy lush green lawn that you’ll need Nitrogen. It’s the building block that promotes the dark green color and the rapid foliage growth, and that it comes in two forms, and both are required .

Being such a strong promoter of growth also means you have to be pretty careful when applying it, as it can be “hot”. If you apply too much you can definitely burn your lawn.

Understanding the balance

Plants need all three elements, and in the correct balance. Each nutrient is a unique component of the building block for growth – let’s look at the next number, the “P” – Phosphorous….

P – Phosphorus

The P in the N-P-K

Phosphorous, commonly called “phosphate” actually is naturally occurring in most soils, but in a form that is not really available for the plants feeding system, and has to be supplemented with a form that is more readily available.

Phosphate is the element that promotes vigorous root development in lawns, essential if the lawn enters a period of stress, such as a prolonged dry spell.

Most phosphorus is actually mined from the soil, and is the result of the combination of mother nature and time converting bird poop into a “phosphate rock deposit” that we extract by mining. In it’s natural form phosphate rock releases very little P, but once reacted chemically, it changes into a form that IS released into the soil, ready for plants to uptake.

Central Florida has immense deposits of phosphate rock, originating as bird droppings on an ocean floor millions of years ago.

Remember the balance.

Many areas have become almost saturated with phosphorous, more because it’s a naturally occurring soil element & quite slow to release, versus a result of over use as a fertilizer. There is concern of it run off from the soil, and it entering waterways and streams etc., and subsequently a threat to water life.

In fact many local jurisdictions are looking at a ban of phosphate use. A better solution than an outright ban however would be a mandatory soil test to determine the correct rate for application.

However, as the second number, phosphorus is usually the lower one, and most lawn fertilizer companies will formulate a blend that is proportionately correct to the other nutrients, and there is no reason for concern if the label is read and it’s used correctly.

K – Potassium

The K in the N-P-K

Finally the third of the three common elements is the “K”, or Potassium, sometimes called Potash. Like phosphate, potash is a naturally occurring rock found throughout the world, but primarily in the Northern Hemisphere. Immense deposits are in Western Canada and Russia.

Potash is generally mined in traditional deep underground mines, though more recently “solution mining” is becoming popular. Potash (K) is an element that is widely used in almost all agricultural areas of the world.

Potassium actually enables the plant to better utilize Nitrogen, as well as helping in the synthesis of a wide variety of plant processes.

Did you know that a lawn grown with optimum levels of potassium will have an improved tolerance to many turf diseases.

While some soils have naturally high levels of potassium, most do not, so generally it’s quite safe to apply potassium to all lawns. Unlike phosphorus a build up of potash should have no negative effects, and it wont leach or run off.

Potash rock is actually a salt, is liberally used in many “ice melt” applications, and is a critical component in ice melt sand mix used by municipalities for sanding roads in our northern winters.

Leave a comment

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