Fertilizer Numbers

Making Sense of Fertilizer Numbers

You have probably seen the fertilizer numbers displayed on the side of bags and wondered what they mean.  Until you get serious about your garden, you might always rely on one of the store workers to help you make sense of which fertilizer you need for your garden.  Of course, this requires you to put your trust in some kid at a store who may have little more knowledge than you do.



You are much better off coming to a basic understanding of what the numbers mean and how they generally apply to your garden.  This will give you a foundation on which to build your knowledge so you can at least be able to question the information you might be receiving from the so-called “expert” at your nursery or garden store.

Fertilizer Numbers

When it comes to fertilizer numbers, you need to think of them in terms of the Big Three.  The Big Three of fertilizer numbers are nitrogen, phosphorous, and potassium, abbreviated by their periodic table symbols, “N,” “P,” “K” on the government mandated label.  N and P are probably obvious to you, but if you have forgotten your high school chemistry course, you might have forgotten that potassium is abbreviated with a K.  Why?  Because the Latin name for what we call potassium, is “kalium.” 

Some people refer to the fertilizer numbers collectively as the NPK numbers.  Depending on what you are hoping to do, each number gives tells you whether the fertilizer can help you.  Some fertilizers help your flowers to strengthen and grow, while others protect your garden from pests.  Matching the fertilizer to your needs can mean the difference between a healthy garden and wilting, unhealthy flowers.

So how do nitrogen, phosphorous and potassium, help you with your garden?

Phosphorous Rich Fertilizer

Of the three numbers, sometimes listed for example as 24-10-8, the middle number is percentage of phosphorous in the type of fertilizer in the mix you are purchasing.  In the numbers for my example above, there would be 10% or one-tenth part phosphorous.  The reason I start with phosphorous and not nitrogen is because phosphorous is what you too should start with if you are just starting to grow grass or most plants.  Phosphorous is great for establishing a strong root structure in most plants so that they get a healthy start.

Nitrogen Rich Fertilizer

Nitrogen is the first number that bags list.  In my example above the percentage of nitrogen is 24%--so it is almost a quarter nitrogen.  Nitrogen rich fertilizer, on the other hand, is more for when your plant has already broken through the surface and is starting to grow in earnest.  In most plants, such a fertilizer will help hasten this growth and to help the plant produce chlorophyll that in turn helps most plant to take on that verdant healthy glow.  Green thumbs also know that nitrogen will create bigger, more vibrant, blooms from most flowering plants.

Potassium Rich Fertilizer

The final number of the three is potassium.  In the example above, it would be eight.  That means that 8% is fertilizer.  (You will no doubt notice at this point that this does not add up to 100%.  This is because most mixes include other ingredients that help the Big Three have the intended effects.  Many are set up for specific types of plants and will add ingredients that help with specific plants.

As to potassium, its main purpose for most plants is to help provide a protective layer against various types of pests.  So more often than not, it is applied to full grown plants.

Now that you have the basics, you can now have a basic groundwork for growing your knowledge of fertilizer and growing those big beautiful flowers that will impress your neighbors and friends.