By John Monzingo, Assistant County Agent, LSU AgCenter

As an Extension Agent, one of the most frequent questions I hear is: “Can I use 13-13-13 or 8-8-8?”

My first response is usually, “Yes, you can use whatever fertilizer you’d like.” But I immediately follow
up with another question:

“What does your soil test say?”

More often than not, the answer is, “I’ve never had my soil tested.” This is usually followed by, “I use
13-13-13 because that’s what I’ve always done.”

This tells me two things:
1. Many people have never tested their soil.
2. Many do not fully understand what those numbers on the fertilizer bag mean.

Let me be clear—I’m not criticizing 13-13-13 or 8-8-8. I’m simply using them as examples.

What Do the Numbers Mean?

The numbers on a fertilizer bag represent N-P-K, the three essential nutrients plants need:
N (Nitrogen): Promotes plant vigor and growth. It’s what makes plants green.
P (Phosphorus): Stimulates root development.
K (Potassium): Improves overall plant health, including disease and drought tolerance.

When you see 13-13-13, it means the fertilizer contains 13% nitrogen, 13% phosphorus, and 13%
potassium by weight. In other words, for every 100 pounds of fertilizer, you are getting 13 pounds
of each nutrient.

Do not Forget Soil pH

Another critical factor in plant health is soil pH, which measures acidity or alkalinity. Most plants
prefer a pH between 6.5 and 7.5, which is considered neutral.

There are exceptions:

Blueberries and azaleas thrive in acidic soil (pH 4.5–5.5).

Proper pH ensures plants can absorb nutrients effectively. In Claiborne and Webster Parishes, soils
often run acidic. To correct this, we use lime, which raises soil pH. Keep in mind, lime takes 3–6
months to fully adjust pH.

So, How Do You Know What Your Soil Needs?

The answer is simple: Get a soil test.

Here is how:
1. Contact your local Extension office for a soil test kit.
2. Using a shovel, collect soil samples about 3 inches deep from 8–10 random spots in your
yard or garden.
3. Mix the samples in a clean bucket.
4. Place the mixture in the provided bag and mail it.

Your results will tell you exactly what nutrients and amendments your soil needs. If you have
questions, your local county agent is here to help.

Bottom line: Fertilizer is important, but soil testing is the key to healthy plants and efficient
nutrient use. Do not guess—test!

If you have any questions, please feel free to contact me, John Monzingo, at 318-927-3110.
It is the policy of the Louisiana Cooperative Extension Service that no person shall be subject to
discrimination on the grounds of race, color, national origin, gender, religion, age, or disability.