Why Soil Testing is Important

Home Grown  by Keith Reed
All gardeners spend lots of time thinking about and working with plants. Unfortunately, not all gardeners give as much attention to their soil. A healthy garden soil is probably the single most important factor (at least among those that the gardener has some control) in determining the potential success of a garden.

A simple soil test is the best place to begin improving your garden soil. If you are a regular reader of Extension gardening information, you have heard us talk about this many, many times. Part of the reason for this repetitive discussion is a result of our looking at hundreds of soil test results each year in combination with some of the basic fertilizer questions we are asked.

For residents of Payne County, a few trends quickly emerge when looking at multiple soil test results. First a quick review: A fertilizer with a 20-5-10 analysis means the product contains 20% nitrogen (N), 5% phosphorus (P), and 10% potassium (K).

The vast majority of area gardeners do not need to be adding phosphorus to their soil. This is especially true if you have been using a garden center staple such as 10-20-10 for years. Phosphorus gets black marks for causing problems with runoff into our rivers and lakes. In 2012, at least 11 states had some kind of restriction on the application of phosphorus as a fertilizer because of this problem. As Oklahomans, let’s not force that on ourselves. Unless your soil test says you need phosphorus, please do not apply it.

Another common issue is soil pH outside the range for optimal growing conditions. The majority of garden and landscape plants perform best in a relatively narrow range of between 6 and 7.5. In the Payne County office, we regularly see pH values between 4.2 and 8.6. At these extremes, fertilizer application is a waste of resources as some critical nutrients are not available to the plant, no matter the fertilizer rate. At this point, pH correction must occur for healthy growth. This can be done relatively easily through the application of lime (if the pH is too low) or sulfur (if too high).

While application of lime or sulfur are straightforward, it does take some time (months) for these changes to begin to occur. In other words, right now is an excellent time to take a soil sample for your garden or landscape if you have not done so in a few years.

For more information on this or any other horticultural topic, you can contact Keith Reed, the Horticulturist in the Payne County Extension office. Keith can be reached via email at
keith.reed@okstate.edu, phone at 405-747-8320, or in person at the Payne County Extension office, located at 315 W. 6th in Stillwater.

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