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What is a Soil Test & Why Do You Need One?

Updated on December 13, 2017
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Caren White is a Master Gardener and instructor at Home Gardeners School. She has been a volunteer at Rutgers Gardens for over a decade.


Before starting any garden or landscaping, it's important to have a soil test performed. A soil test will give you a snapshot of the pH of your soil and the level of nutrients available. This is critical for plant health. Before you go out and spend money on fertilizer that you may or may not need, call your local extension office and request a soil test kit.

Avoid store-bought kits

You should always use the soil test kits and soil-testing laboratory recommended by your local extension office rather than the cheap soil test kits you see on store shelves. Store-bought soil test kits are not always accurate and the soil samples used are too small to get a clear picture of your yard or garden. It is worth it to pay more for a soil lab to do the testing. A larger sample will be tested under laboratory conditions resulting in more accurate results. The lab will also send you a written report of the results along with recommendations for any soil amendments. You don't get that from a store-bought kit!

Use the right tools

The tools you use to take your soil samples are important. You can use any kind of digging tool such as a shovel or a garden trowel as long as it is not made of brass, bronze or galvanized metal. These metals contain copper or zinc which can contaminate your samples. Use a plastic rather than metal bucket to mix your samples for the same reason. Clean the bucket before using especially if it has previously been filled with fertilizer or other chemicals that might contaminate your samples.

How to sample

You will need to dig 10 to 12 small holes for a large area such as a lawn or 6 to 8 holes for a smaller are such as a vegetable garden. If you are testing your vegetable garden, take samples from every part of the garden. If you are testing your lawn, make sure you sample the front, back and sides of your lawn.

The soil samples should be taken at the depth of the roots of the plants that will be growing in that area. For a lawn, that means holes 3 inches deep. For a garden, vegetable or flower, you will need to dig 6 to 8 inches. Mix the soil from all of your samples in your bucket to get a good representative example of the soil in your yard. Then place the soil in the container provided with the kit, fill out the enclosed forms and send it off to the local laboratory.

Lab results

The laboratory will be looking at the pH level of your soil as well as the levels of phosphorous, potassium, magnesium and calcium. Garden plants grow best in a pH of 5.5 to 7.0. If your soil pH is outside of the range, your plants may not be able to access nutrients that they need to grow. After analysis, the soil lab will send you a report that tells you what your pH is and the amounts of phosphorous, potassium, magnesium and calcium in your soil. The report will contain recommendations for the appropriate amendments to add to your soil to optimize it for your lawn or garden.

Test every three years in the fall

You should repeat your soil test every three years to make sure that your soil remains at the correct pH and the nutrients are at the correct levels for your lawn and garden. Fall is the best time to take you soil test because the amendments you add will have all winter to be incorporated into your soil.


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