Do a Soil Test for Your Garden

Testing soil in your garden is a good idea. Knowing the quality of your soil is the best forecast of plant success. If you know you have good soil, you should expect good plant results. If you know you have poor soil, you shouldn’t be surprised by poor growth. To determine the quality of your soil you can grow a garden for years and see how it turns out, or you can have the soil tested.

There are two basic ways to test soil: buy a home test kit and do it yourself or send a soil sample to a laboratory and have it done professionally. The best answer is to have the pros do it.

A laboratory analysis only runs about $20 for a basic test, but can run much higher if you want to test for specific elements. Generally, a home gardener only needs to know four things about soil: the pH, and the levels of nitrogen, phosphorus, and potassium (or potash). I would recommend a fifth, the level of organic matter. Basic professional testing by a university or private lab should include all of that info plus salinity levels. You can find a list of testing labs at this link to Colorado State University fact sheet 0.520, Selecting an Analytical Laboratory. Results should be send back to you in a few weeks.

A home soil test kit usually costs about half the price and can be done quickly. It will give you the same basic information, but not nearly as accurately as a laboratory test. Most home kits work best for acid soils and are less accurate for alkaline soils, but they’ll still give you a basic idea of soil quality. A slightly inaccurate test is better than no test at all.

A home soil test kit

If you are just starting your garden and have a plot of bare soil, I highly recommend getting a professional soil test. That way you’ll know exactly what you need to add to the soil in the way of amendments and fertilizers to prepare it for the type of plants you plan to grow. If your garden is in place and you’re just concerned about basic nutrient levels, a home soil test kit will give you an basic, though not precise, idea of what is in your yard.

To begin either test you need to gather samples of soil from your garden. With a clean trowel or spoon, dig a hole in four to six locations about four to six inches deep. You’re getting a soil sample at root level. In a typical garden plot collect five samples, one from each corner and one from the middle. For your average soil status, combine the soil samples into one bag. If you really want to know how the soil differs from one end of your garden to the other, you can do multiple tests.

Collecting a soil sample

Bag the combined sample and send it to the laboratory per their specific directions for submitting soil. Or carry it to your kitchen or shed for a do-it-yourself test.

The basic process for doing a home soil test kit is to combine your soil with distilled water and various chemical tablets in small plastic vials. You’ll use different tablets in different vials for different test steps. The water will change color and you compare the color with a chart to determine the respective test result.

Don’t expect accurate results. The outcome of my pH test showed it to be somewhere between 6.0 and 7.0, not too extreme. Depending on how you interpret the color, it could be close to either end. That’s good enough for most plants, but if you’re trying to grow something with specific pH needs you’d be better served by an accurate reading.

Interpreting soil pH results

The other tests showed similar vague results and weren’t surprising. I already knew my soil was deficient in nitrogen, phosphorus, and potassium. That’s why I’m amending it and adding fertilizer. But based on the home soil test kit I don’t know how much fertilizer is enough, or too much. Many professional soil tests will provide guidance on how to add nutrients.

Checking soil test results

A home kit is best suited for determining if the location you’ve chosen for your garden is appropriate. If you find that one location is extremely poor while another is average, you can save time and effort by gardening in the location that is less work.

Regardless of whether you do it yourself or have it done by the lab experts, get a soil test done. A professional test is advised. It will keep you from guessing about plant problems. It will help you provide appropriate levels of fertilization. It will set a foundation for proper soil amending.

By knowing your soil you are better able to know your garden. Eighty percent of plant problems are soil related. Understand your soil and you have a great advantage in understanding why things go wrong with your plants.

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