Soil sampling important for gardens

The warm weather at the beginning of the new year started many gardeners thinking about their gardens. I started looking at my records from last year, and I am in the process of planning where each type of vegetable will go in the garden.

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But before the first vegetable seed or plant is put in the ground, I need to know what the nutrient levels in the soil are. I can find this out by having my soil tested. A soil test will help you develop and maintain a more productive soil by providing information about the fertility status of your soil. Also, the soil test will help you select the proper liming and fertilization program.

I receive numerous questions on why to have soil sampled, where and how to take the sample, and how often it should be sampled. There are a number of reasons to sample your soil.

The first is to determine the pH of the soil and what nutrients are present. If the soil pH is low, adding lime to the soil will raise the pH. Lime takes time to change the pH of the soil. Pellet lime has some small particles that will start working within a few days, but the majority of the lime will take a couple of months to work. So the soil should be sampled early in case additional lime is needed.

The second reason for sampling is the high cost of fertilizers. In previous years, a 50-pound bag of 10-10-10 fertilizer was available for around $10. Someone told me the other day that he paid $20 for a 50-pound bag. Also, adding more fertilizer than the plants can use could lead to the nitrogen and phosphorus running off into our streams and lakes and causing excess algae, which decreases water quality.

Another reason to have soil tested is that the University of Georgia College of Agriculture and Environmental Science will make a fertilizer recommendation based on specific crops that you are trying to grow. If you are trying to grow azaleas, we will recommend an analysis of fertilizer to use, and recommend the times of the year to apply the fertilizer to the plant.

The next question is where and how to sample. One of the more important steps in soil sampling is collecting the sample. Soil test results can be no better than the sample submitted to the laboratory for analysis.

A soil sample needs to be a composite sample from different areas of the yard or garden. If I were to take a sample of soil from one spot in the yard and move over two feet and take another sample, the odds are that I would get two completely different results. The best way to take a sample is to take 10 to 15 random samples and mix them together in a clean bucket.

To take the sample, use a clean trowel or spade. Push the tool to the desired depth and push forward. This will create a wide space in the soil. Cut a thin slice of soil about one-quarter of an inch thick and two inches wide to the desired depth. The desired depth depends on what you are growing. For lawns, the sample should be four inches deep; for vegetable garden, shrubs, and trees, the sample should be six inches deep. Remove any grass, thatch or mulch from the sample.

Once all the spots have been sampled, mix them well and remove enough to fill to the line on a soil sample bag available from my office or at some garden centers. On the soil bag, fill out the name, address, sample number and crop. If there is more than one sample, write down where the samples came from in your yard. List a crop on the bag. The crop could be centipede grass, azaleas, apples or vegetables. It needs to be specific so we can send a fertilizer recommendation.

How many soil samples are needed for a yard? A soil sample can cover a large area if the soil is uniform. However, if the soil has been amended in flower beds or vegetable gardens, those should be put in separate bags. If there is an area that is not doing as well as the rest of the planting, sample it and the good area separately to compare the results.

How often should soil be sampled? We have gardeners who soil sample every year. How often you sample will depend on the results. If the soil is low in all the elements, it should be tested the next year.

Once the nutrient levels are at medium to high levels, the soil can be tested every two to three years. Vegetable gardens tend to change more than other crops, so every year or every other year is best.

Soil samples are very affordable compared to the cost of fertilizer. It cost $8 to have a sample run, and they can be dropped off at my office at Savannah Rapids Pavilion.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/