Question: How can gardeners collect good soil samples for good results?

Answer: Soil test reports provide information that is useful in making decisions about any needed lime and fertilizer. Because the test report is used in making these decisions, a gardener needs and expects reliable results. The reliability of the soil test, however, is no better than the sample submitted. To insure reliable and accurate soil test results, it is important to correctly collect samples that represent your soil.

The first step is to determine where to collect the soil samples. Do not make the assumption that the soil is the same throughout the entire area. Many factors can cause variations in the soil. You will need to collect separate soil samples for each area that is different. Consider collecting separate soil samples in areas that are obviously different in slope, color, texture, drainage, and/or vegetative growth. On new home sites, soil variations can exist due to soil being moved around or brought in to fill low areas. You also need to take into consideration collecting separate soil samples for areas with different uses. For example, you would want to collect a separate soil sample for your lawn area, vegetable garden, and shrubbery area because each area is managed differently. When collecting soil samples, avoid small areas where soil conditions are different from the rest of the area to avoid false results. Examples include wet areas, places where wood or debris has been burned, fencerows, compost piles, and severely eroded areas.

Now that you know where you are going to collect your soil samples, you need to collect the soil samples correctly. Collecting a good soil sample will result in an accurate report that is reflective of the soil in the designated area. Every soil sample you submit should consist of about 6 to 10 cores taken at random locations throughout the defined area. If a probe is not available, a shovel and trowel will work. Collect your samples with stainless steel, chrome-plated, or plastic tools and place samples in a clean plastic bucket. Avoid using tools that are galvanized and buckets made of aluminum, brass, or bronze because they could possibly contaminate the sample with traces of micronutrients. Tools and buckets should be clean and free of lime, fertilizer, and soil from the last sample collected to prevent contamination and inaccurate results.

Move leaves, mulch, and other debris from the soil surface. Samples collected in recently tilled soils should be taken to the depth the soil has been tilled. For established lawns, collect samples 4 inches deep. For vegetable gardens and flowerbeds, take samples 6 to 8 inches deep, and for trees and shrubs, sample to a depth of 6 to 10 inches. It is best not to sample immediately after applying lime, fertilizer, compost, or manure to prevent skewed results. Avoid sampling when the soil is wet because wet soil could damage the soil sample box during shipment. Test the soil several months before planting because the soil test report will make recommendations for the next growing season.

Place the 6 to 10 cores in a plastic bucket and break up the cores, remove rocks, and thoroughly mix the sample. Before placing the soil in the box, it is generally easier to write on the box while it is still folded flat. The three digit identifying number you write on the box should be recorded so that when you receive your results you will know which identification number represents which area. Each sample must be submitted in a standard soil sample box and accompanied by a completed form. These boxes and forms are available at the Sampson County Extension Office. Do not put the soil in a plastic bag and do not tape the box. Boxes should be approximately two-thirds full. On the form indicate the plant to be grown with the appropriate crop code. Lime and fertilizer recommendations are made on the basis of the plant’s needs, so it is essential to provide this information. Instead of using commercial horticultural crop codes, gardeners should use ones for lawn, garden, and ornamentals so that recommendations are easier to use on a small scale.

Samples can be mailed directly to the North Carolina Department of Agriculture or brought to the Extension office. The speed at which soil test results become available varies with the time of the year. Turnaround time in the summer is shorter than in late fall or early winter. When you receive your soil test report, it will include measurements obtained from your soil sample along with recommendations. The Extension Office has information available to assist in interpreting your soil test report.

By following these recommendations and collecting soil samples correctly, your soil test report will be a representation of the soil in your area. With accurate soil test reports, recommendations of what the soil needs will be more reliable and you can amend your soil to improve or maintain your plant’s health.

Reminder: A new program for 2012 is the “Sampson County Friends of Horticulture.” This program offers monthly “How To” Horticultural Seminars. Please call (910) 592-7161 for more information. Please turn your radio to WCLN 1170AM every Monday, Wednesday, and Friday at noon (that’s lunch time) and listen to the Sampson County Ag Minute segment, which is brought to you by the Sampson County Extension Agricultural Agents. Please call the Sampson County Cooperative Extension Center at (910) 592-7161 with your horticultural questions and to register for any upcoming events. Be sure to check out the Ask An Expert Widget at sampson.ces.ncsu.edu for any questions you may have.