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

Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.

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What is a Soil Test?

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. Too much or too little of any nutrient can be the difference between success or failure. 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.

Why Should You Use a Professional Soil Testing Laboratory?

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 entire 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 amendments needed to optimize your soil. You don’t get that from a store-bought kit.

Using the correct tools will ensure the accuracy of your soil test.

Using the correct tools will ensure the accuracy of your soil test.

What Tools are Needed to Collect Your Soil Sample?

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 to avoid contaminating your samples.

When taking soil samples in your lawn, make sure that you collect them from every part of your lawn.

When taking soil samples in your lawn, make sure that you collect them from every part of your lawn.

How To Correctly Take Soil Samples

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 area 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 lawn in your front yard, back yard and side yards.

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, either 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.

What Will the Soil Test Results Tell Me?

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.

My Experience with Soil Testing

I had the soil in my vegetable garden tested because I noticed that the plants were large and lush, but my harvest was small. This usually indicates too much nitrogen which encourages foliage growth and too little phosphorous which is critical for vegetable and fruit production. The soil test report confirmed my suspicions and suggested I add bone meal, a source of phosphorous, to my garden. I chose Jobe’s Organics Bone Meal because it is organic and high quality. I applied it at the rate suggested by the report in the fall so that it would have all winter to be incorporated into my soil. Sure enough, the following summer my garden was producing many more vegetables than the previous year.

Fall is the best time to have your soil tested and to add the recommended amendments to your lawn or garden.

Fall is the best time to have your soil tested and to add the recommended amendments to your lawn or garden.

You Should Test Your Soil Every 3 Years

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.

© 2014 Caren White