How To Read A Bag of Fertilizer

March 07, 2013

Whether you're at the home store trying to choose a bag of fertilizer, or looking at the report from a lawn service describing what they applied to your lawn, a little understanding goes a long way. 

N-P-K

FertilizationSomewhere on that bag of fertilizer, or lawn service report, you are going to find three numbers with dashes “-” in between. For example, a lawn service might list 16-4-8 for the fertilizer component of an application. Or, a bag of fertilizer at the home store might show the numbers 15-0-15.

These numbers show the percentage of different types of nutrients in the fertilizer. The first number (N) is for the Nitrogen component; the second number (P) is for the Phosphorous; the third number (K) is for potassium. Why “K” for Potassium? That's the standard chemical symbol for it.

So for a listing of 16-4-8, the fertilizer was 16% nitrogen, 4% phosphorous, 8% potassium. On a bag of fertilizer showing 15-0-15, the composition is 15% nitrogen, 0% phosphorous, 15% potassium.

These three elements are the key nutrients that all plants need to grow and thrive.

What to look for in the fertlizer isle

The next time you are at the home store, take a walk down the fertilizer aisle in the garden department. As you first look at all the options, you can see that there are fertilizers for lawns, for trees and shrubs, for roses, for tulips ... not to mention “all-purpose” and “starter” fertilizer.

When you actually pick up a bag or a box and look a little closer, here's what you will discover: from one product to the next, all that really changes is the picture on the package … and the ratios of the nutrients. The ratio that is right for your lawn depends on the time of year and your type of grass. For example, you will generally want to apply higher nitrogen rates in the spring and lower in the fall. We strongly recommend having a soil test done by your local extension office or soil lab so that you can know exactly what your lawn is lacking, what it may have to much of, and what you need to do to get it in balance. With fertilizer, too much can be just as big (if not bigger) an issue than not enough.

For the most part, the N-P-K ratios are the whole difference from bag to bag. Trees do not get some completely different set of nutrients than lawns or roses. Now, to be fair, there are minor additives in specific formulations for tomatoes (calcium) or rhododendrons (acidifiers), or any number of other specific applications. In the end, though, each product is mostly N-P-K with other minors (and sometimes sand and other useless additives) making up the rest of the percentage.

So what does my lawn need, and how would I know?

It depends, of course, but a soil test is a great place to start!

One of the easiest things and most economical things you can do is hire a lawn service to come out and apply their program of services to your lawn. On the one hand, they will have a system that they think works pretty well for lawns in your area. On the other, it can be tough to customize these programs to your specific type of grass and challenges and sometimes these companies will have a "one plan fits all" attitude towards lawn care that can cause issues. Be sure to ask questions, and keep in mind that the lowest price is usually not going to be the best service or option.

You can also go to your local big box store or landscape supply company and look for a fertilizer brand that has different products developed for different times of the year. Simply follow the steps, and you will generally be pretty good to go as long as you know the type of grass in your yard. These companies have spent a lot of time and money figuring out what lawns want and need. As you go along, you will learn more and more about what is in those products and how why they work.

If you are using one of our varieties, be sure to check out our Seasonal Maintenance Videos on our Turf Talk Blog and the maintenance page for each of our grasses on our site for general fertility recommendations. If you still have questions, send us a message on our Sod Solutions facebook page and one of our turf pros will be more than happy to answer your question.