Decoding Fertilizer

 In Articles

By Joel Marchel Jr.

Your yard can be an intimidating task especially once you are confronted with a bag of fertilizer that has three numbers that you have no idea what they mean.  Ask someone about the numbers and you will just get words thrown at you such as: Nitrogen, Phosphorous and Potassium; leaving you wondering what language they are speaking and how it translates.

Fertilizer is food for your plants.  Like the nutrition information on the food you eat, the numbers on the fertilizer bag will tell you what you are feeding your plant and what you will get in return for your investment.

Those three numbers have to be there by law and are called the Fertilizer’s Analysis.  They indicate, respectively, the percentage of Nitrogen, Phosphorous and Potassium in the fertilizer.  Each of those three macro-nutrients can and will do something very important for your plants.

Nitrogen promotes thick leafy green color and growth.

Phosphorous promotes healthy root system, flower, and fruit growth.

Potassium helps with a plant’s endurance and vitality.


If the numbers are percentages why don’t the equal %100?

20-10-10? But that only adds up to 40%, what else am I putting into my yard and garden?

Most likely the remaining portion of your fertilizer has micro-nutrients, or ingredients that help with the even spreading of fertilizer or both.  To avoid spreading the fertilizer unevenly and having unattractive brown spots or dense patches of extreme growth; a fertilizer includes ingredients that make sure a uniform layer of fertilizer will go over the desired area and give you the best look possible.

What fertilizer should I use?

To begin, try to avoid an extremely focused fertilizer such as 35-0-02.  Rather, your fertilizer should have a little bit of the described macro-nutrients.

Healthy lawns need

a Nitrogen strong fertilizer.  The Nitrogen will give your lawn that deep, lush, green look and help it remain healthy while naturally resisting weeds.

Starting lawn – and generally any starting plants for that matter – a good even fertilizer is best.  Something like 20-10-10  or 16-16-16 will give your new flora the best chance at a healthy life.

Flowering plants and vegetables will need a Phosphorous rich fertilizer.  The Phosphorous will help your plants root system and ensure that the flowers /produce grow in more beautiful than ever.

Trees need a Nitrogen heavy fertilizer; 16-4-8 will be the best.

If in doubt, 16-16-16 or something close, is always a safe bet for all plants, trees, and vegetables until you learn a little more about what you need.

How do I know what nutrients my soil is lacking?

In order to know what nutrients your soil needs you will need a sample of your soil tested.  You will have to send away a sample of your soil and the testing process generally takes ten days.  This testing will cost approximately fifteen dollars.  It is best to get your soil tested once every few years.

What is the difference between organic and synthesis fertilizers?

Organic fertilizers are, more often than not, slower to release and have a much lower concentration of nutrients [Nitrogen, Phosphorous and Potassium] than synthesis fertilizers.  Synthesis fertilizers are usually much cheaper than organic fertilizers and have to be applied fewer times a year.

What is the difference between fertilizers and soil amendments?

By definition a fertilizer must have a high concentration of nutrients in order to help plants growth and health; however a soil amendment’s purpose is to actually change and help the soil, such as structure, drainage and microbes, and actually have little nutritional value.

What are slow release fertilizers?

Slow release fertilizers [ex. fertilizer spikes] are covered in a material that slows the release of the nutrient and can evenly give the plants nutrients over time.  They are considered too expensive for general use.


1)         Fertilizer By The Numbers – By Patrick St. John

2)         Fertilizer Basics – Bachman’s Floral, Gift, and Garden

3)         What Do The Numbers On The Bag Of Fertilizer Mean? – By Allyn Paul

4)         Basics On Tree Fertilization -By Steve Nix

Recommended Posts

Start typing and press Enter to search