Since we are about to enter our prime growing season in full force, it’s a good time to talk about fertilizer. Fertilizer can be pretty confusing because of the variety and types of fertilizer. You have the organics and the synthetics, and then what about all those numbers on each bag? Let’s try and break some of that down.

First let’s talk about the numbers you see on each bag like 19-19-19. These numbers are there to tell you the nutrient content of that particular fertilizer. In this example, this fertilizer would contain 19% nitrogen, 19% phosphorus, and 19% potassium. One of the more popular fertilizers you’ll see in the store is marked 32-4-0, meaning 32% nitrogen, 4% phosphorus, and 0% potassium.

So why do they come up with all these different variations to confuse everyone when all you want to do is purchase some fertilizer for your lawn or garden? Well, it’s because you need different amounts of those nutrients for different circumstances, and there might be a little bit of marketing happening as well. So why are they primarily talking about nitrogen, phosphorus, and potassium? Here’s why.

Nitrogen, phosphorus, and potassium are the three major nutrients we are concerned about in our soil. There are other nutrients, but they tend to take care of themselves unless you have been making a lot of demands of your soil over a period of time since these nutrients are needed in lesser amounts.

The way we like to explain it is by using a lawnmower as an example. Our lawnmowers need a couple of additives to work properly, or work at all actually. They need gas and oil. In the lawnmower/garden metaphor, the gasoline would be the equivalent of nitrogen and the oil would be equivalent of phosphorus and potassium. Gasoline gets consumed by the lawnmower like nitrogen gets consumed by your plants. As we mow the yard, we need to add gasoline for the lawnmower to do what it’s supposed to do in the same way we need to add nitrogen to help the plants keep doing what they are supposed to do.

In the lawnmower, as long as the oil is at the proper level, the mower works as intended. Similar to the way your garden works as intended with proper phosphorus and potassium levels.

Now imagine you didn’t have a way to measure how much gas or oil you had in your lawnmower. How would you know how much it needed and when it needed it. Fortunately, we have simple ways to address this issue. It’s the same with our soil. We have soil tests that will provide us with the existing nutrient levels in our soil, so we know how much we need or how much we don’t need to add to our soil.

Fortunately, soil tests are inexpensive and are a great way for us to keep from under or over applying these nutrients to the soil. To find out more about soil testing and how to get your soil tested, go to our website and click on the Hot Topics button. You’ll find instructions there on how to gather your soil sample. Once you get it ready, just bring it to the Tulsa County OSU Extension. Good luck. Photo: Tom Ingram