How to Take a Soil Sample
Why should you test your soil? Knowing exactly how much and what kind of nutrients it needs will save you money and protect the water system. If you know your soil's deficiencies, you can buy what's required, and you can apply the nutrients your plants will use. That means you won't spend cash on unnecessary (and often expensive) soil amendments. And you won't apply too much, causing fertilizer run-off that pollutes the creeks, streams, and other waterways in your community.
Home gardeners only need to have their soil tested once every three years. Depending upon where you live, a test may cost anywhere from $8 to $15. County Extension Offices in some states, like Arkansas, offer soil testing as a free service. Residents in many states, however, must pay nominal fees to independent labs.
Scroll down now to learn how to
- prepare a soil sample for testing.
- locate a soil testing center near you (even if you’re an organic gardener).
- read your test results.
Three Steps in Preparing a Soil Sample
Step 1: Collect soil.
Take soil from eight or more locations within the testing area. For instance, if you're trying to determine the fertility of your lawn, collect soil from various places within it. If you plan to test your vegetable garden, collect soil from your garden only. Don't mix soils from different areas in your yard, such as the flower bed, the lawn, and the vegetable garden. Doing so will skew the test results, and you won't learn what each area of your landscape needs in order for plants to thrive.
Use a trowel, a shovel, or a specially made soil sampler so that you can scoop down into the soil horizon about six inches. When taking soil samples from a flower bed, scrape away mulch first.
Place each small sample in a clean plastic bucket. Don't use a rusty or galvanized bucket, or a bucket that has been used to hold cleaning products. Residual traces of chemicals and/or metals may affect test results.
Once you've collected a good number of samples, it's time to mix them.
Step 2: Mix it.
Mix the samples together for about a minute with your hand. Discard rocks and other debris, as well as worms. If you've taken samples from your lawn, be sure to remove turf, too. The soil should not be wet. If it is, allow it to dry before performing the next step.
Step 3: Prepare it for the testing lab.
Place one to two cups of the mixed soil in the paper bag or cardboard container supplied by the testing lab. Make sure the soil reaches the fill line. If you don't have a container from the lab, put the soil in an unused paper bag, Ziploc bag, or clean Mason jar.
Clearly mark the outside of the container with your name and the date. Also indicate where the soil came from in your yard. This is particularly important if you're submitting three separate samples, which is typical for most home gardeners. For instance, one sample might be marked "garden," another "lawn," and another "flower bed."
To see just how easy taking a sample is, watch the short video above from the University of Maryland Home and Garden Information Center. To view other soil sample videos, move your cursor across the bottom of the video screen once the clip begins.
Although the lab facilities discussed in each video are state specific, the information about fertility and soil sampling is valuable for every gardener.
If you plan to take lots of soil samples, consider trading in your trowel for a sampler. A soil sampler makes getting six inches down into the soil horizon much easier.
Locating a Soil-Testing Lab in Your Area
The Cooperative Extension Agencies of the United States Department of Agriculture (USDA) are a great source of information for home gardeners located in the U.S. Through your state Cooperative Extension office, you can learn the best plants and the best planting times for your region.
Your extension office can also provide you with a list of local authorized soil testing labs. Find an extension office near you, or check out the USDA websites links to reliable soil testing labs.
These traditional testing labs will perform a standard soil test on your sample. You'll learn your soil's pH level as well as how high or low your soil's levels of plant-available nutrients are. And you'll receive valuable recommendations for the type and amount of fertilizer needed for optimal growth.
Labs for Organic Gardeners
If you're an organic farmer, a standard test is of little use. It won't provide organic fertilizer recommendations. For that, you'll need to send your sample to an alternative soil testing lab. For the names and contact information of alternative labs in the U.S., visit the National Sustainable Agriculture Information Service website.
You might also opt to purchase your own testing equipment and test your soil at home. Test kits that measure soil nutrients as well as pH levels are readily available online and in home-garden stores.
How to Read Your Results
Most test results include at least three pieces of helpful information: 1) the general levels of nutrients in your soil, 2) your soil's pH level, and 3) specific fertilizer recommendations.
General Nutrient Status
Although test results vary from lab to lab, most include a graph that tells you the general level of important nutrients in your soil, such as phosphorus, potassium, magnesium, calcium, sulfur, zinc, manganese, iron, copper, boron, and sodium. Levels are usually marked as excessive or very high, optimum or high, medium, and low or very low.
Test results also include your soil's pH level. pH is a measurement of soil's sourness (acidity) or sweetness. The pH scale ranges from 0 to 14. Although individual plants have specific pH preferences, in general blueberries, azaleas, rhododendrons, and conifers are acid-lovers that like pH levels of 5 to 5.5 best. Vegetables and turf prefer more neutral pH in the 6-7 range. Getting the pH level right is vital to plant performance as it directly impacts the availability of nutrients in the soil to plants.
Most importantly, soil test results include recommendations (in lbs.) of fertilizer you should apply per 1,000 square feet. To raise pH levels, lime is often recommended.