What’s in your soil?
If you don’t know, you’re taking a chance on the health of your plants, whether they’re the trees in your yard, the grass in your lawn or the flowers or vegetables in your garden.
What’s more, you could be throwing away money, wasting effort and harming the environment.
Your plants depend on the soil and its components for survival. And the only way to know the state of that soil is to have it tested.
A soil test is an indicator of its health, just as a medical test is a barometer of yours. A basic laboratory test shows the nutrients in the soil as well as its acidity or alkalinity, a factor that determines whether those nutrients are available for the plants’ use.
Now is a good time of year to test your soil, since fall is the best time for adding certain amendments to improve soil health.
You can’t tell what soil contains just by observing it. Sure, you can see its color and feel its texture, but you can’t judge whether the soil has, say, enough nitrogen or too much lead.
If your plants don’t get what they need from the soil, they’ll become stressed, explained Jacqueline Kowalski, agriculture and natural resources educator with the Ohio State University Extension in Cuyahoga County. Plants under stress are more susceptible to pests and diseases, which take work and often money to treat — if you’re successful. If not, you’ll be laying out even more money for new plants.
So why not just fertilize the heck out of them?
For one thing, that would involve unnecessary expense. For another, overfertilizing can add too many soluble salts to the soil, drawing moisture away from plants and possibly stressing or even killing them, said Gary Horrisberger, manager of Holmes Laboratory, a private testing laboratory near Winesburg.
What’s more, excess nutrients can leach or run off into the water supply, causing all manner of environmental mayhem.
Sometimes soil tests can guard the health of people, not just plants.
Tests can detect the presence of heavy metals, which can be toxic. Those metals are sometimes found in or near old industrial sites, and in vacant lots where old buildings were razed but materials were left behind, Kowalski said. Inner-city land is particularly vulnerable.
You’d definitely want to test the soil before planting food in such an area. You’d also want to test before building a playground or other facility where children might touch the soil.
In those cases, Kowalski said it’s important to choose a laboratory that uses methods specified by the U.S. Environmental Protection Agency.
Who should do the test?
Kowalski recommends either a university or commercial laboratory.
You can do it yourself using a home test kit, but know that some kits tell you only the soil’s pH level (that is, its acidity or alkalinity). A home kit may seem like a bargain because it contains supplies for multiple tests, but Kowalski doesn’t recommend reusing the same kit over several years. If it’s not stored properly, the kit may degrade, she said.
Kowalski said sending a soil sample to a soil-testing laboratory will give you more accurate readings. Perhaps more importantly, the lab will give you recommendations for fixing problems in your soil, such as telling you what type of fertilizer or amendment to add and in what quantity.
Labs typically ask you what you’re growing so they can tailor their recommendations to the specific plants’ needs. A lawn, for example, has different requirements from a cornfield or a perennial bed, and the lab will take those requirements into consideration. If you’re changing a plot’s use, tell the lab what you grew during the past year and what you want to grow there next year, Horrisberger said.
While the numbers and chemical terms in a soil test report can seem daunting to a typical gardener, most labs explain the data and offer their recommendations in plain language, Kowalski said. Commonly they’ll tell you what to apply and how much, usually expressed in pounds per 1,000 square feet.
Sometimes a lab will have a sample report on its website, so you can see what you’ll be getting.
What kind of test?
In most home situations, a standard soil test will tell you everything you need to know, said Jon Dahl, manager of the Soil and Plant Nutrient Laboratory at Michigan State University.
Standard tests usually cost $10 to $25.
What’s included in a standard test can vary. Typically it measures pH and the levels of phosphorus, potassium, calcium and magnesium in the soil. Sometimes it includes the amount of organic matter and some fairly technical issues, such as cation-exchange capacity and base saturation. (Don’t worry about what those mean. Remember, the lab should explain the results in plain language.)
If you notice problems with plants, such as leaves that are off-color or striped when they’re not supposed to be, you might consider a supplemental micronutrient test, Dahl said. That test tells you the soil’s level of nutrients that are used by plants in tiny quantities.
However, he cautioned that such a test will tell you only the micronutrients’ status in the soil. It can’t tell you whether those nutrients are actually getting into the plants. A plant tissue analysis might give you a more accurate picture, he said.
How to take soil samples
Labs differ on how they want you to submit samples, so call or check the lab’s website first to find out the sampling requirements.
Some will send you a container for submitting a soil sample. Others will accept a sample in a plastic bag.
When you’re taking samples, think of your yard in terms of zones, Kowalski said. Your lawn might be one zone, your vegetable garden another zone, your perennial border a third. If you have a problem area, such as a part of your yard that doesn’t drain well, consider that a zone all its own, she recommended.
Take eight or 10 samples from each zone, mix together the soil from all the samples in that zone and then send a portion of the mixture to the lab.
Why so many samples? You have a better chance of getting an accurate picture, Kowalski said. It’s especially important to take a generous number of samples in an area that might be contaminated, she said, because a contaminant can be limited to just a small section of the property.
To dig a sample, use a clean trowel or spade, dig down into the soil about 6 inches, and cut about a 1-inch-wide vertical slice of soil. For lawns, remove the thatch and roots first before digging, Kowalski said.
Put all the samples from a zone into a clean bucket, and pick out debris, such as pebbles and sticks. Let the soil air dry overnight, break up the clumps and then package about 2 cups of the composite sample for shipping, or whatever amount your lab requires.
How often should you test?
Kowalski recommended testing every two to three years. You can test more often if you grow plants that are heavy feeders or you just want to keep a close eye on your soil’s fertility.
Most people test their soil either in the fall or the spring. Fall is a good time, because amendments such as manure or lime that are added now will have the winter to break down, Dahl noted.
However, he said what season you choose isn’t as important as always testing at the same time of year — that is, always in the spring or always in the fall.
That way, you’ll get a more accurate picture if you want to track long-term trends in your soil, he said. Nutrient levels are lower right after the growing season than in the spring, so it’s better to compare samplings from the same season.
Mary Beth Breckenridge can be reached at 330-996-3756 or email@example.com. You can also become a fan on Facebook, follow her on Twitter @MBBreckenridge and read her blog at marybeth.ohio.com.