Edible Landscaping

How To: Soil Test

Testing your soil every three to four years gives you a snapshot on its health.

To get the most accurate results, dig many holes in your garden, mix the soil together, and take a sample of your soil sample to send away to a testing laboratory.

Add soil amendments in fall, based on the test, so they can break down over the winter and have their desired effects by spring.

If you read any good gardening book or article about soil, eventually the author is going to recommend you do a soil test. But what is a soil test and why is it important? Are soil tests just like other "should do" things in our life, such as going to see the doctor yearly even if you aren't sick?

Well, soil tests do serve a purpose. They certainly aren't the "be all and end all" of information about your soil’s fertility, but they can provide a window into the health of your soil. And as I've said many times, a healthy soil results in a healthy garden. Even if your garden is thriving and the plants growing strong, a soil test every 3 to 4 years gives you a baseline of results to help you monitor changes in your soil.

Here are some tips and techniques on how to best use a soil test to make your soil even better for growing plants.

Fall for Testing – Autumn is a good time of year to test your soil. The nutrients are usually at their lowest levels and soil labs aren't as busy as in the spring. Just be sure to test your soil the same time of year each time you test or you might get very different results.

DIY or Labs – Whether you test the soil yourself or send it away to a lab depends on the amount of detail you need. Home test kits are handy, inexpensive, quick and accurate, but they won't give you the level of detail of a soil lab report. Home tests often use color coding to match the results with soil solution. They usually just check for pH and major nutrients such as phosphorous and potassium. Soil labs (usually at the state land grant university) will give you results for pH, organic matter, phosphorous, potassium, calcium, and cation exchange capacity, along with recommendations for adjusting your soil's fertility as needed. You can even request special tests for heavy metal contaminants or micronutrients. Though not very expensive (usually less than $50), you do have to collect a sample, bring or send it in, and wait for results.

Know What You're Testing For – The recommendations for adjusting the soil's fertility will vary depending on what you're growing. You'll need to take separate samples for various crops such as tree fruits, berry bushes, and vegetables. This may get a little pricey if sending the sample away, but each crop has different needs that will be reflected in the lab recommendations.

Spread it Around – When taking soil samples for testing make sure you get a representative mix. Dig a number of small holes around the area that will be planted. Take a small trowel full of soil from beneath the sod and place it in a bucket. Make 8 to 10 test holes in a 1000 square foot area to get a good sample for testing. When finished, mix up the soil in the bucket and take a sample of the sample to send off. This way you'll get results that will work for all the soil in the garden area.

Interpreting the Results – While most soil labs will send a narrative description of your soil's health and recommendations for any needed amendments, it's good to know what it all means. Labs may give numbers and some will create charts to show you the optimum levels and where your soil stands. Underneath they will give recommendations for regular and organic fertilizers. Often the recommendations are given for a 1000 square foot garden. You can adjust these based on the size of your garden.

Work it Now – While fall is a good time to do a soil test, it's also a good time to amend your soil, especially if you're using organic materials that are slow to break down. Add manure, compost, lime, sulfur, and granular organic fertilizers based on the soil test. When applied in fall, they have a number of months to slowly degrade, so by spring when you're ready to plant, your soil should be up to snuff.

More articles on soil testing:

Soil Testing
It's Time to Lime
Building Great Soil

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