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- Proper soil sampling important for useful test results
Thomas J. Koske, Young, John, Gill, Daniel J., Owings, Allen D.
By LSU AgCenter Horticulturists Dan Gill, Tom Koske, Allen Owings and John Young
Many home gardeners are aware that a soil test is a good practice to determine the soil’s nutrient status, pH and other characteristics. Most of us, however, do not know the proper procedures for taking soil samples, which can make the test results inconclusive.
The LSU AgCenter’s soil test report has been designed so the chemical analysis provides useful numbers for the client. The results, however, are only as good as the sample. Landscape beds should be sampled separately from lawn areas. Soils that differ in appearance, plant growth or past treatment should be sampled separately if those areas are large enough to be fertilized separately.
For each sample, collect soil plugs from about 10 or more places in each sampling area or block. Use a zigzag pattern to take a good, representative sample. Mix the plugs thoroughly before filling a sample carton or container that is mailed to the soil test lab. A pint of soil is the recommended amount.
Because the soil test results reflect the area sampled, avoid sampling unusual areas unless you specifically want to examine those spots. A bad spot is not representative of the larger, normal area.
Sample to the depth for the kind of plants you want to grow. For lawns and landscape beds, sample to a depth of 4-6 inches.
Most test results will indicate levels of phosphorus, potassium, calcium, sulfur and magnesium. All of these nutrients are essential for plant growth. The analysis will indicate whether these nutrients are present in low, medium, high or very high amounts.
The report also includes the sodium concentration. This element is not essential for plant growth and is harmful at high levels. Low sodium is optimum.
Soil acidity, called pH, is another measure on the report. For most ornamental plants grown in Louisiana, a soil pH of 5.5-6.5 is ideal. Acid-loving plants like azaleas prefer the 5.0-5.5 range. Most ornamental plants do not like a soil pH above 7.0.
For lawns, centipede grass prefers an acid soil of 5.0-6.0 pH, while St. Augustine, Bermuda and zoysia grasses prefer a higher soil pH of 6.0-7.2.
The LSU AgCenter’s Soil Testing and Plant Analysis Lab is located on the LSU campus in Baton Rouge. You can obtain forms and information on sample submission from the lab’s Web site at www.lsuagcenter.com/stpal/. The cost for testing is $7, and several plants can be listed for one sample if they all will be grown in the sampled zone.
Come to LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is located near the intersection of Burbank Drive and Nicholson Drive (La. Highway 30) in Baton Rouge across the street from the new LSU baseball stadium. Go online to Louisiana Yards and Neighborhoods for additional information.
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Editor: Mark Claesgens