Soil tests for home lawns and gardens in Iowa can be submitted to neighboring state universities and private laboratories. Soil tests are not available from Iowa State University.
Where can I submit a soil sample for testing?
Many soil testing laboratories offer specialized soil tests tailored to agronomic (field) crops and commercial growers. Soil tests for home gardeners and commercial growers are conducted similarly; however, when conducted for field crops, the report includes recommendations that do not apply to home gardeners.
Always select a soil testing lab that provides recommendations for the home garden, lawn, or vegetable garden.
Any one of the soil testing labs listed can be selected. Compare costs, processing times, location, and/or available services to choose the best lab for your needs.
The following university laboratories provide soil test results for home garden and lawn settings.
- University of Minnesota Soil Testing Laboratory
- University of Wisconsin Soil & Forage Analysis Lab
- Michigan State University Soil and Plant Nutrient Laboratory
The following private laboratories provide soil tests with recommendations specific to garden and lawn settings. This is not a complete list of laboratories, and no endorsement is implied. Please contact us if you wish to add a soil testing lab to this list.
- Waypoint Analytical
- Frontier Labs
- SoilWise – AgSource Soil Testing
- A&L Great Lakes Laboratories
- Midwest Laboratories
- Dairyland Laboratories
- SoilKit
How do I collect a sample?
All of the laboratories listed above provide detailed instructions on their websites on collecting and submitting a sample to their lab.
A soil sample is a mixture of many small samples collected from 10-15 locations across the area to be tested. Use a small trowel to collect the samples from the top 4 to 8 inches of soil and mix them together. Avoid including soil from the very top layer of the soil profile, as well as any compost, mulch, roots, or manure, as it can skew the soil test results. The soil testing laboratory's website provides more information on the size of the sample required and how to label and submit it.
In general, soil samples should represent areas managed similarly or areas where the same crops/plants are grown. If you wish to test soil in different settings, submit separate samples for separate tests. For example, conduct one soil test for your vegetable garden and a separate test for the lawn or perennial border. If areas are large or have different environmental conditions, conducting separate tests for specific areas is beneficial. For example, a shady and wet front lawn with heavy, clay-based soils should be tested separately from a sunny, well-drained lawn in the backyard.
When do I collect a sample?
For most gardeners, fall or early spring is the best time to conduct a soil test, as it allows time for soil amendments to be added before the next growing season. However, a soil sample can be collected at any time when the soil is not frozen. Do not collect soil samples in excessively wet or dry soil conditions or just after applying lime, fertilizer, compost, or manure.
What is evaluated in a soil test?
Most basic soil tests report the levels of phosphorus, potassium, pH, and organic matter (%). Often, they include or allow the option to add-on tests for lead, soluble salts, and other nutrients, such as calcium, magnesium, sulfur, boron, and micronutrients.
Some laboratories will also provide the soil texture class (percentage of sand, silt, and clay) as part of the test or as an add-on. Nitrate levels can also be measured, but the results require more interpretation because nitrogen's behavior in the soil is complex. Select laboratories can test for contaminants such as heavy metals or herbicides, but these tests often require specialized processing and additional costs. Occasionally, tests can also provide a soil microbial analysis, telling you the biomass of bacteria, fungi, protozoa, and nematodes in the soil sample.
Once I submit a sample, what can I expect?
Most labs process samples in one to two weeks and provide an analysis and recommendations, often electronically and sometimes as a hard copy. Labs will provide recommendations based on the information you provide related to the type of plants growing in that area.
Once I receive the report for my soil test, what do I do?
All the laboratories listed above will provide recommendations based on the specific garden setting (e.g., lawn, vegetable garden) or the plants being grown in that area. Some give this as part of their analysis; others charge extra for the recommendations. As a homeowner, it is highly recommended that you select a test that provides recommendations for the lawn and garden.
The test results typically include information about soil fertility, pH level, and/or problems caused by excessive salts or fertilizer materials. Recommendations for appropriate fertilizer rates are provided to ensure optimal conditions for plant growth without adverse environmental effects. Click here to see a sample report from one of the labs.
How to Interpret Soil Test Results
The laboratories listed above also provide resources on their websites, including instructions on how to read their reports and calculate fertilizer requirements based on these reports. Utilize the report, accompanying recommendations, and the lab's online resources to apply fertilizers and soil amendments at the appropriate rate.
How often should I conduct a soil test?
Home gardeners benefit from testing soil every 3 to 5 years or when problems with plant growth or health are observed.
Can I use a home soil test kit?
Many home soil test kits are available for use in the home garden. These test kits are inferior to those tests conducted by a laboratory. Several factors contribute to their inaccuracy. Most home test kits test for only a few nutrients/conditions - typically nitrogen, phosphorous, potassium, and pH. The results of these tests are often presented in very general terms, such as "low," "medium," or "high," or they require a comparison of a color to a color gradient, which can be subjective and inaccurate. The reagents used to perform the test can quickly expire and may not be an appropriate type of test for the soil in your area (there is more than one method that can be used to determine nutrients like phosphorous in the soil, and the best one to use depends on other factors like pH).
In contrast, laboratory soil tests provide more precise and accurate results, giving values in a unit of measurement rather than a general term like "high" or a shade of pink or blue that must be compared to a color scale. They test for a broader range of soil nutrients and conditions using trusted and accurate methods that are appropriate for your soil conditions. Most importantly, nearly all laboratory soil tests provide recommendations on actions to take based on the test results. These recommendations are extremely valuable, as most home gardeners are unfamiliar with interpreting soil test results or calculating the necessary amendment or fertilizer rates needed to correct soil deficiencies.
More information can be found in this article from Montana State University: Soil Testing: Test Kits vs. Laboratory Analysis.
Where can I get a soil test done for larger commercial operations?
For larger commercial crops (i.e., agronomic crops, acreages, row crops, small grains, hay, pasture, commercial vegetable growers, orchards, etc.), clients should use soil testing labs that maintain certification through the Iowa Department of Agriculture and Land Stewardship (IDALS). For certification, labs must use specified testing procedures and prove consistent results. IDALS conducts blind soil sample tests through these labs regularly. This list can change over time as labs may occasionally fail the blind tests, but can return to the list once they become compliant again.
Approved soil testing labs can be found at this website: IDALS Commercial Feed and Fertilizer Bureau - Commercial Fertilizer.
Click on "Certified Soil Testing Laboratories" found under "Soil Testing."
More Information
- Managing Garden Soil
- How to Change Your Soil's pH
- Fertilizing in the Home Garden
- Lawn Fertilization
- How to Calculate Fertilizer Rates for Lawn and Garden
- Soil Test Interpretations and Fertilizer Management for Lawns, Turf, Gardens, and Landscape Plants, University of Minnesota (PDF)
- Soils - Iowa's Nature Series (PDF)
- Introduction to Soil Science
Photo credits: 1: Microgen/AdobeStock; 2: Aaron Steil; 3: Madelaine/AdobeStock