Fall is an excellent time to reflect on the past growing season and look toward next spring’s gardening opportunities with the lessons from this year in mind.  I often look back with spite on the insects and pathogens that caused problems or ruined crops, but there is one aspect of our gardens that is often overlooked and my underlie many of the problems we experience….. our soils! 

As experienced gardeners, we know that soils need attention to remain productive, but how often have you taken a quantitative measure of soil fertility and other soil attributes?  A soil test is an excellent way to gauge current soil productivity, discover soil issues, and plan for maintenance of soil health through addition of appropriate soil amendments.  These tests are relatively inexpensive and provide valuable knowledge and insight into our soils.

Since we live in such a wonderfully productive agricultural area, we are lucky enough to have an abundance of soil testing labs.  Agricultural Soil Management, Inc. and Waypoint Analytical Illinois, Inc. are both located right here in Champaign-Urbana and provide soil testing for lawns, trees and home gardens, as well as large scale agricultural producers.  This week, I spoke with agronomists at both companies to understand more about what home gardeners should be concerned with when considering soil testing.

“Gardners are very concerned with yield, just like large-scale farmers.  It is important to consider soil, so you can determine what amendments are needed, or if they even need to add any,” said Alec Bean, agronomist with Agricultural Soil Management, Inc. 

Andy Wycislo is an agronomist with Waypoint Analytical, Inc.  Wycislo echoed Bean’s comment, “In most cases, garden soil may be OK, but you never know without a test. I’ve seen instances where folks have over fertilized and some nutrient levels are through the roof.” 

Over fertilization and the subsequent offsite movement of excess nutrients into our streams and rivers is a major water quality issue nationwide.  Although a large amount of this non-point source pollution is typically attributed to industry, it is still important for smaller-scale lawn and garden applications to stay within recommended limits.  In recent years, some research has shown alarmingly high levels of nutrient runoff from urban areas.  One way we, as home gardeners, can address this water quality concern is through the use of soil tests and proper fertilizer applications.

Both of the local soil testing labs mentioned above provide soil test results, along with interpretations that can be used to estimate appropriate fertilizer application amounts.   If you are wondering how to apply these interpretations to the management of your particular garden soils, call your soil testing lab. 

“We are more than happy to talk with folks and discuss their soil test results,” said Alec Bean. 

Agronomists, like Bean and Wycislo, and other experts on staff at most soil labs are available to discuss the results in detail and help you diagnose soil problems to make management decisions. 

To collect soil samples for testing, you must first decide which areas within your lawn or garden have similar management activities or issues that need to be addressed.  Do you have an area where plants showed signs of nutrient deficiencies last year?  If so, provide samples from that area separately from healthy areas.  You can then compare test results from both areas. Are you planning a different crop rotation in one portion of your garden compared to the other? Since the management practices will differ in these two areas, plan to test them separately.

Soil samples should be collected from across each sampling unit and combined to make a composite sample.  You can do this by taking small individual samples from the top 6-8 inches of soil (the area most garden plant roots use) at evenly distributed points across your sampling unit.  Combine all of the samples into a plastic bucket and mix the soil well.  

“Don’t use a metal bucket or a rusty old spade. Galvanized products will add zinc and skew test results,” noted Wycislo. It is important to use a plastic bucket as metal (especially rusty metal) can contaminate your samples.   

Once you have mixed up your composite sample, take out about one cup of the mixture to submit to the lab.  Place it in a plastic bag, label it, and send it in to the lab.  Results are typically available within 1-2 weeks of submission.

The University of Illinois Extension maintains a list of Illinois soil testing labs available at:  https://extension.illinois.edu/soiltest/.  Please consult this listing to find labs in your area.  And don’t be shy, give these folks a call if you have questions about how to sample or after you receive your results.  They are local soils experts with a wealth of knowledge to share!

Ryan Pankau is Horticulture Extension Educator with University of Illinois Extension serving Champaign, Ford, Iroquois, and Vermilion Counties.