FOR RELEASE January 4, 2010

                            GARDENING WITH
                         ARANSAS/SAN PATRICIO
                           MASTER GARDENERS


By Robert Moore, Master Gardener, Aransas/San Patricio Master Gardeners

Testing your soil is very important for several reasons. First, unless you have had your soil analyzed, you are simply guessing when applying fertilizer. Over-fertilizing is actually worse for your plant’s health, than under-fertilizing, but both are bad.

In the Texas Coastal Bend, it is common for soils to contain sufficient potassium (P) and phosphorous (K), but not enough nitrogen (N), whether your soil is sand or clay, or both. Why? Because nitrogen is volatile and is reduced by both air and water, while potassium and phosphorous are not. Therefore, if you apply a “complete” (N,P, K) fertilizer, you can be wasting money and harming your plants. The build up of very high levels of potassium and/or phosphorous can restrict plant uptake of micronutrients and kill them. The only way to know is to find out what is already down there and learn the ‘language’ of plants.

Soil tests are simple to perform. They come with easy-to-read instructions and are easy to submit. Texas soil sample containers, instructions and forms are available from your local Texas AgriLife Extension office. The costs per sample submitted are: Regular Test - $10, Regular plus Micronutrients - $15; Regular plus Organic Matter - $20 and Regular plus Micronutrients and Organic Matter - $25. You will submit the sample you gather through the mail to the address indicated along with the payment. The test report is received in about 2 weeks and is sent directly to you.

Your local library has lots of information about soil. If you have an on-line computer, the Internet has a lot more information than you could ever want. This article is concerned with practical issues rather than technical information. First, your soil is likely to extend down a lot farther than you will ever dig. To set a limit on the depth of soil you should be concerned with, the key word is root-zone, which is the depth that your plants reach into the soil for moisture, air and nutrients.

The second important factor with regard to soil testing is obtaining a proper soil sample from the root zone. Following the simple instructions, multiple small holes are dug and the ‘slices’ are combined and mixed, then placed in the sample bag to the “fill” line. Look at and feel the soil that your roots live in. Do you think they like their home soil? Is it brown and does it smell good?– or is it hard clay? – or just sand? - sand to 6”- 8” and then clay? None of these? Make these basic observations about what kind of soil you have as you take your sample, it will help you know how to improve it.

Sand holds a lot of air, but does not hold moisture or nutrients well. Clay holds both water and nutrients, but almost no air. Roots need the right mix of all three to thrive. Aha – THRIVE - not just ‘survive’. For optimum growth and production of flowers and fruit and healthy, happy plants, soil is the major factor because air, water and nutrients MUST be available at ROOT level. Below root level is not important. If water and nutrients leach below roots, the plant will not benefit.

Organic matter holds all three key elements – air, water and nutrients. Pay a few extra bucks to obtain the percentage of organic material on the soil test report. If the percentage of organics in the top foot of your dirt is less than 10%, that is the most likely cause of consistent plant problems and can make the difference between plants that ‘survive’ and those that THRIVE. Look at photos of plants in magazines. Do your plants look like those? If not; why not? Comparing photos of what they SHOULD look like and in reality is an effective way to tell if the plants need your help by amending the dirt or mulching.

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A third important soil test result is pH – a short term for the measure of acidity and alkalinity of your soil. If pH is too low or too high for optimum growth of your plants, they will suffer. When you receive the soil sample test results, look closely at the pH number. Look up the (scientific) name of your plant and find out what soil pH it prefers to THRIVE. If the pH number from your soil sample is different, your can effect pH in the location of that particular plant by adding the right kind of organic matter or other amendment. Dig a hole, mix in the amendment – simple and effective. The plant’s roots will find the amended soil and show their appreciation by looking more like the pictures.

Another few dollars well spent would be if you requested an analysis of the micronutrients in your soil sample. The resulting list in your test results will show you if any micronutrients are deficient in the soil sample.

Many soil test results show a vertical line called “Critical Level” which does NOT mean ‘too high’. Critical Level means “just right” or the proper level. This level is critical to achieve, i.e. the GOAL. In addition, unless a salinity-specific salt analysis is requested, only a conductivity result is offered in test results, which is not particularly helpful to the average layman gardener, in determining the level of potential salt damage to vegetation growing in that soil.

OK – let’s get down to ‘brass tacks’. A soil test report will make a fertilizer recommendation for how many pounds of N, P, and K you should add per 1000 square feet (or expressed per acre if you asked for crop analysis). If you need assistance in converting the information to something meaningful for your yard consult the fertilizer calculator at the AgriLife Extension - Aransas County Office website at or call or visit a Master Gardener at the local AgriLife Extension. You can also take your soil sample to your favorite local plant nursery.

Now let’s deal with the last major issue - amending soil with “organic material” There are lots of different kinds of organic matter, but only one that will do you much good - humus (Latin for “earth, ground”). Go to the library or look it up online. The USDA site has information about soil humus at Humus is very important. Do not just bury grass, leaves or manure. That would be a bad move that could possibly kill your plants. The best source of humus is fresh compost. Not just any compost, but high-humus compost. Humus is stable. It will no longer decompose and may last for several centuries. It is a long-term ‘fix’. Humus is called the “life-blood” of soil .The best part is that you can make your own – for free – at home. But have your soil analyzed first. That is the starting point and the beginning of a new journey.

© Robert C. Moore ~ All Rights Reserved

The Texas AgriLife Extension Service - Aransas County Office can be reached by phone at 361 790-0103 or by email at and is located at 611 E Mimosa, Rockport, TX 78382.

AgriLife Extension education programs serve people of all ages, regardless of socioeconomic level, race, color, sex, religion, handicap or national origin.

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