One of the challenges we face as gardeners (and there are many) is knowing what fertilizer to use and how much to apply. This process is complicated by the fact that fertilizers come in a variety of formulas.

More often than not, gardeners follow a general rule of thumb for application that may have worked one year, or maybe their neighbor told them about, or perhaps they read something online that seemed to make sense. The problem with rules of thumb is that oftentimes we end up whacking out thumb with the hammer. In reality, we need to know the nutrient levels in our soil before we can accurately add supplemental fertilizers.

Fortunately, there is an easy solution to find out the nutrient levels of your soil and that’s the soil test. Yes, you can order do-it-yourself soil tests online, but for my money, and it’s not much money ($10 for a soil test) OSU can test your soil and tell you what you need to know, and fall is a perfect time to get your soil tested.

The basic soil test (and that’s really all most of us will ever need) will tell you soil pH, and nutrient levels of nitrogen, phosphorus, and potassium. We call nitrogen, phosphorus, and potassium the primary nutrients found in soil. There are a variety of other secondary and micronutrients, but for the most part, the micro-nutrients tend to take care of themselves since they are not needed in large quantities. There are additional tests to detect the levels of these secondary and micronutrients should you still have issues in your garden after you get the basic soil chemistry in line, but this would be the exception to the norm.

We call nitrogen a “mobile” nutrient while phosphorus and potassium are called “immobile” nutrients. Immobile nutrients tend to take longer to change in the soil which makes fall a great time to test since you can add the needed amendments now which gives them more time to be in place and available for the vegetables in your garden next year. We have instructions on how to get your soil test on our website in the Hot Topics and Soil sections.

Basically, you’ll need to get a bucket, gather up 15 to 20 scoops of soil, mix them together in the bucket, get a plastic sandwich bag, and fill it with your soil sample. Once you have your sample ready, just drop it off at our office… and of course, pay the $10 fee. In about two weeks, you will get your results back with recommendations on how to amend your soil to the proper nutrient levels and if you do it now, you’ll get a jumpstart on next year’s growing season. 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 courtesy OSU Ag. Comm.