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Gardening: The importance of soil sampling to prevent nutrient deficiency

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During the cold winter months, there may seem like there is little to do in the garden, but that is not the case.

One of the most important things to do, especially before planting anything, is getting a soil test. Now is the best time to test the soil before we begin planting and fertilizing.

Standard soil tests provide a wealth of information about what is missing from the soil as well as what is already there in abundance. Many problems in the garden can be avoided by proper preparation before plants go into the ground.

Taking a soil sample is rather simple. It is imperative to identify similar areas in terms of what plants are growing or will be grown. A large front lawn, for example, that is only growing turf grass, may only need one test for the entire area. A bed of annuals, however, may need a separate test from the shrubs next to it. It is best to understand what type of soil plants like to understand how to group the tests.

Taking a sample is fairly straightforward. Once the area to be tested is identified, you will want to take soil from 6 inches deep in random locations throughout the area.

For the most accurate results, take soil from eight different spots. Mix the soil together and put it into whatever container the soil lab you are using requires. Clemson Extension offers soil testing and will generally provide the sample bags needed, but due to the closure of county offices, you may use any sealable bag.

For these samples, please provide a minimum of two cups of dry soil and be sure to label all bags. You also will need the requisite form with your information, as well as the list of plants you will be growing.

Send soil samples, along with the $6 fee for each test, to Clemson Agricultural Service Laboratory, 171 Old Cherry Road, Clemson, SC 29631. 

Chlorosis on Citrus from nutrient deficiency 2

Pictured is chlorosis on a citrus plant caused by a nutrient deficiency.

Understanding a soil test can be a little bit more complicated.

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The first, and arguably the most important, aspect is the pH. The pH is the measure of hydrogen ions within the soil, but for most gardeners, it is the measurement that shows how acidic or alkaline the soil is. The pH is important because of how it affects the availability of certain nutrients within the soil. And certain plants have a preference for a specific pH and will struggle significantly if it is off.

Gardening

Newly planted camellias need acidic soil to thrive. 

Plants such as azaleas, camellias and hollies, all prefer a more acidic soil while plants such as pecans and certain vegetables prefer a more neutral pH. Adjusting the pH of the soil takes time and therefore should be started well before planting into the ground.

Blueberries, which require a pH of around five (acidic), will be stunted if the pH is too alkaline when establishing and will generally not recover.

There also are several key nutrients essential for plants to grow that can be tested. Nutrients such as phosphorus and calcium are required for growth but can be excess within our soils, so it is imperative to know before fertilizing as this can create a toxicity. Though only needed in smaller amounts, nutrients such as magnesium and manganese are critical for healthy palms and cycads.

Fruit trees such as citrus and pecans require zinc and can decline if this is deficient. Most tests will provide a breakdown of the nutrient analysis, which will help determine the amount and types of fertilizer needed for the specific plants. One of the nutrients not included is nitrogen. Though nitrogen is one of the most important, it is also the hardest to quantify due to its mobility in the soil.

Magnesium Deficiency of Gardenia

Pictured, a magnesium deficiency in a gardenia plant.

It is important to have your soil tested, if for nothing else, to know what is lacking and what you do not need to add. Soil tests are only a measure of the mineral components of the soil and do not determine the overall health of the soil itself. It is best for a healthy soil to follow the best practices of improving the soil, as well not just adding fertilizer. 

For more information about soil testing, visit hgic.clemson.edu/factsheet/soil-testing

Christopher Burtt is the Urban Horticulture Extension Agent and Master Gardener Coordinator for Berkeley, Charleston and Dorchester counties. He can be reached by email at cburtt@clemson.edu

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