What To Know About Soil Testing

I’ve been helping professional turf managers manage their fields and grounds for over 40 years. I’ve also helped teach lawn owners the importance of keeping the soil under their feet healthy and vibrant. It all starts with the soil, whether you’re growing bluegrass or bluebonnets.

Why Get Your Lawn Soil Tested?

Soils are dynamic. Like us, sometimes they’re robust, healthy and active. Other times, they’re not doing so great. Much of this depends on structure, chemistry and nutrition. Testing will identify issues your soil may have and provide the information necessary to create a plan to correct them. This makes your soil perform better and allows it to support whatever you’re growing in it better. Remember, soil is pretty much a living, breathing thing! It can get “sick” just like we can.

What Are You Testing Soil For?

Typically, we are testing for four basic things.

Soil pH

measures acidity or alkalinity in soil on a scale from zero to 14, with 7 being neutral. Soil pHs below 7 are considered acidic (sour) and those above 7 are called alkaline (sweet). Most lawn grasses prefer a soil pH in the 6.0 to 7.0 range, although some will thrive in lower or higher pHs.

An imbalanced soil pH can tie up nutrients in the soil making them unavailable for grass roots to absorb. Adjusting soil pH is possible, but it’s not always easy and takes time. Reach out to your local extension office for help on this.

Cation Exchange Capacity

Paying attention to the cation exchange capacity (CEC) value of soil test results will give you an idea of how sandy or heavy your soil is. Why is this important? In short, this number helps measure the soil’s capacity to hold nutrients. The lower the CEC, say 10, the “lighter” the soil is and the fewer nutrients it can hold. Most of these nutrients get flushed through the soil. Higher CECs, like say 24, are heavier (clayey) soils that hold more nutrients and water. However, these heavier, high CEC soils typically have less pore space to hold moisture and oxygen and can be difficult to work with.

Nutrients

Nutrients in the soil can be accurately measured using a soil test. Your lawn and gardens use three major nutrients: nitrogen (N), phosphorus (P) and potassium (K). These are the nutrients they use in the greatest quantities. Other nutrients like calcium, magnesium, sulfur, iron, boron, zinc and manganese, are no less important; they just aren’t required in large amounts. Because of this, there are usually adequate amounts of them in native soils.

Nitrogen levels in the soil are extremely dynamic and are seldom tested. When fertilizing your lawn, you’ll want to use a fertilizer with nitrogen every time. Nitrogen is the most important nutrient required by your lawn. Pay close attention to phosphorus and potassium levels, too.

Phosphorus helps build a robust root system, whether you’re growing grass, flowers or vegetables. Potassium helps increase stress resistance, whether it comes from disease, shade, heavy traffic or winter hardiness. Both phosphorus and potassium play key roles in plants that bear fruit or vegetables.

Organic Matter

A healthy, vibrant soil contains a small amount of organic matter, usually in the 3-4% range. Organic matter is made up of decomposing roots, leaves, clippings, etc. It helps feed beneficial bacteria and fungi in your soil. These microscopic bugs are the key ingredients in your soil keeping it healthy. Organic matter improves your soil’s capacity to store nutrients and improves soil structure, too. You’ll want to pay attention to this value.

How to Sample Your Soil

Taking soil samples from your lawn or garden is easy by following these basic steps:

1. Using a small shovel or soil probe, randomly collect 10-15 soil samples from your lawn. Samples should be taken from the top 3-4 inches of soil. Remove the thatch or live material from each sample.
2. Collect these samples in a pail or other container and mix them thoroughly.
3. Transfer about one cup of soil into a soil sample bag provided by the testing service and identify the sample for future reference.
4. Do not collect soil samples when the soil is wet from rain or irrigation.
5. Multiple samples can be collected if you’re dealing with different soil types or if some areas of a lawn look stressed or need special attention.
6. Return the sample to the soil testing lab or other soil testing service provider.
7. Your test result(s) should be received within one to two weeks.

Soil Testing Options

At-Home Soil Testing

Soil testing kits are available at garden centers, lawn & garden retailers or online. Although convenient and possibly less expensive, they are not as accurate as tests provided by professional labs. These test kits can have a shelf-life, so make sure you’re using a fresh kit.

I’d recommend staying away from at-home soil testing kits. I’ve tried many in the past and the results seem to look very similar regardless of the soil test kit or the soil sample taken. There are some things you can do yourself when it comes to lawn care. Soil testing shouldn’t be one of them.

Soil Testing Lab

Using a professional soil testing lab will yield accurate results that you can trust and will provide accurate data needed to make soil corrections. Some garden centers have relationships with reputable soil labs and can help you get your samples in the hands of a professional. Extension services at your local university or college are the best option. Contact them for information, pricing and the supplies you’ll need to collect the soil samples.

These tests may cost a bit more, but you’ll get an in-depth report and reliable recommendations to consider when planning your fertilizer and amendment needs.

FAQs

What time of year is best for soil testing?

Early spring or late fall are the best times to test soil. Typically, these are the times of the year when most soils are void of fertilizer that you may have added during the growing season. Testing shortly after fertilizing your lawn would skew the results and give a false reading. The key is to test consistently at the same time every year. Also, use the same soil lab each time. Soil labs can use different methods in testing and results may vary.

Are home soil test kits accurate?

If you’re looking for quick results and not necessarily a wealth of information, at-home soil test kits are okay. You’ll get an accurate soil pH reading and some very crude phosphorus and potassium values, but that’s about it.

Nitrogen values in any soil are constantly changing and tests for them only show you what the N value was at the time of testing. These N readings are useless, so ignore those if your kit offers them. These kits have limited value in that they offer no recommendations on how to use this information.

Finally, if you do use them, make sure they are fresh soil testing kits. If they’ve been on the shelf for a year or two, the chemical agents used for testing may be compromised.

How often should I test?

I recommend soil testing every three to five years. If an initial test shows an imbalance in one or more nutrients or if you’re attempting to adjust soil pH, you may want to retest in consecutive years to see if any attempts to improve deficiencies are working.