Soil tests are important for new gardens, changes to your yard
The start of the gardening season, before you start buying plants and digging holes, is a good time for an important checkup: a soil test.
“The chemistry of your soil makes a big difference to your plants,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic of The Morton Arboretum in Lisle. “A laboratory test can give you information to guide you in choosing plants and preventing problems.”
The test will tell you the pH of the soil — how acidic or alkaline it is — which has a large effect on how plants absorb nutrients. Since not all plants thrive in the same pH, it’s important information to have when you go plant shopping. It can also explain some plant problems, such as yellowing leaves on pin oaks, that are often caused by a mismatch between an acid-loving plant and an alkaline soil.
A soil test will assess the levels of the major nutrients that are important to plants, such as potassium and phosphorus. It also can measure the soil’s “cation exchange capacity,” an indication of how well your soil holds nutrients and makes them available to plants.
The right kind of soil test can also check for the presence of toxic heavy metals such as lead — a critical step before digging an edible garden. Lead that accumulated years ago from lead paint or air pollution caused by leaded gasoline can remain in the soil for decades.
“Lead in the soil can be absorbed by food plants that will be eaten by people,” Yiesla said.
Garden centers sometimes sell do-it-yourself kits for testing soil pH, but a laboratory test is more accurate and will give you much more information. A list of soil testing laboratories is available on the Arboretum’s website at mortonarb.org/plant advice.
You will take samples of the soil in your yard and mail them for analysis in packaging provided by the laboratory. Prices start at roughly $25 for simple testing on a single sample, but you may want to ask for more in-depth testing that costs more. Testing for lead, for example, will be more expensive.
It’s best to call a testing laboratory to ask exactly what they test for and how they present their reports, Yiesla said. You will get more use out of a soil test report that clearly explains what the results mean.
Unless you have a very small yard, it’s often worth having samples from three or four areas of the yard tested separately. “The soil can vary quite a bit within a single property,” she said.
The time to get a soil test is when you haven’t done it for several years, when you start gardening in a new place or when you want to make a big change. For example, if you plan to convert some lawn to an edible garden or a perennial bed, a soil test is a good first step.
It’s also a good idea to test when you’re thinking of planting a tree. “Any tree you plant will have to grow in that spot for many years,” Yiesla said. “You want to make sure you get the best match between the kind of tree you choose and the soil it will have to spend its life in.”