I wasn’t really happy with the way my plants grew last year. Do you think I need to add fertilizer and if so, what kind, and how much? DR

There are so many fertilizer options out there, it’s easy to be intimidated when trying to make those decisions. As always, the first step toward healthy plants is the soil and the only way to know what’s going on with our soil is with a soil test. A lawnmower is a good analogy to help understand soil nutrients.

For a lawnmower to function properly, it needs gas and oil. We have simple ways to check the levels of gas and oil in our lawnmowers. We can open the cap and see the gas level and use the dipstick to check the oil level. As long as our mowers have sufficient gas and oil, the mower should be able to accomplish its task.

In the garden, nitrogen is like the gas in our mowers, it provides the plants with the fuel to grow and produce. Phosphorus and potassium are like the oil in our mowers. As long as we keep the level where it should be, the mower should run, depending of course on how much fuel we have. The oil could be perfect, but if the fuel level was low, our mower is going to quit on us before we are done.

In this example, the soil test is our dipstick. Rather than go into detail about how to get a soil test, we have those instruction on our website under the Lawn and Garden Help/Soil section.

Once you get the results back for your soil test, your challenge will then be to select the correct fertilizer to meet the needs of your soil and then apply it in the proper amounts.

When you go out to purchase fertilizer, you will notice three numbers on all the bags of fertilizer. These numbers indicate the amount of fertilizer in each bag. For example, if the bag of fertilizer is labeled 10-20-10, these numbers reflect the level of nutrients in the bag. In this example it would be 10% nitrogen, 20% phosphorus, and 10% potassium. You’ll notice that this only totals out to 40% which tells you the rest of the contents of the fertilizer are inert, binding agents.

So let’s say your soil test showed you were low in nitrogen and made a recommendation that you add 1 pound of nitrogen for every 1000 sq. feet of your garden. And then let’s also assume the soil test said you had appropriate or even excessive levels of phosphorus and potassium. In this case, 10-20-10 would not be a good choice for your fertilizer since you would be adding phosphorus and potassium which were not needed.

If your soil was only low in nitrogen, you should purchase Urea which is marked 49-0-0. This tells you that this product is 49% nitrogen, 0% phosphorus, and 0% potassium. And it tells you that since it is about half nitrogen, you will need 2 pounds of Urea to get to your 1 pound of nitrogen for 1000 square feet. It may sound a little confusing, but once you get the concept, you’ll be good to go.

We have quite a bit of information on our website (www.tulsamastergardeners.org) about fertilizers and soil. Just go to the Lawn and Garden Help Section and click on soil. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: OSU Ag. Communications