If you live in Salt Lake County and have your soil tested, you might notice on the bottom of the report the statement “for further assistance, please see your county agent Katie Wagner”. Well, I am indeed the agent listed so I receive dozens of calls each year from gardeners with questions about soil testing. That being said, I have noticed some common questions that I would like to address in this post – 5 things to know about testing your soil – don’t get testy over soil testing!
Q: Why should I get my soil tested?
A: It is important to have your soil tested to know how to properly care for your garden plants and for the environment. If you are having a hard time growing garden plants or if you want to know how much fertilizer to add to your garden, it is a good idea to have your soil tested. If your plants are all growing well, it is ideal to have your soil tested every 2 to 3 growing seasons, unless you make any major changes (like you add a bunch of new stuff to your garden soil).
Q: What information do soil tests provide gardeners?
A: Soil tests provide gardeners basic information on how much and what types of nutrients to add to plants when fertilizing (N (nitrogen) P (phosphate) K (potash)), soil texture (relative percentage (%) of clay, silt, and sand), soil pH (acidic, neutral, or alkaline), and, in Utah, your soil salinity (amount of water soluble salts in your soil). This could be an incredibly long blog post if I were to talk about how to interpret all these result types so I’m going to make it easy on both you and me. Check out these two online factsheets. They will walk you through how to interpret your soil test reports and how to understand a fertilizer label.
Q: How do I get my soil tested?
A: The best place to start is to visit the USU Analytical Lab at usual.usu.edu. Click on the ‘forms’ tab on the left side and select soil. Read this entire form carefully; it will tell you how to take your soil sample, how much soil you need to collect, and where you should send the sample and payment. I recommend under ‘comments’ to describe the area you are sampling from, like ‘vegetable garden’, and include your email so you are directly emailed results. A routine test is usually sufficient unless you are looking for something in particular (like % organic matter or micronutrient levels). Note – you do not mail your soil sample to your local county Extension office – you must send it up to the USU Analytical Lab on the USU campus (the mailing address is on the top of the form). County Extension offices have soil sampling kits (mailing box, baggie, and form) you can pick-up, but if it is more convenient for you to not have to make an extra trip, just use a spare box you have lying around the house to send up your sample. You must, however, print off the form and fill it out (and include payment) prior to sending your soil sample to be tested. If you mail your sample from your local post office, mark the package ‘soil sample’ to help the mail carrier understand the contents of your package. One more thing, you do not have send moist soil (it is heavier and more expensive to ship), it is fine to allow your soil sample to dry out before sending it (in fact, it is easier for the lab to process if they receive a dry soil sample) and it won’t affect your results.
Q: Will a soil sample tell me what is wrong with my garden?
A: Short answer, probably not. A soil sample gives gardeners information on things that are tested for (soil texture, soil pH, soil salinity, soil nutrient levels N-P-K) but do not expect your soil test report to give recommendations like “Susie, the reason why your tomato plants look sickly is because xyz”. That is not to say that soil tests are not important; they provide important clues for solving the big mystery. For example, a high salinity reading would help explain unhealthy plant growth and should be followed with the question, why is my soil salinity high – from where are the salts originating? This is where your county Extension office can help you interpret your results. By the way, if you are curious about soil salinity, check out the USU Extension fact sheet “Solutions to soil problems – high salinity”
Q: Will a soil test tell me if there is something dangerous in my garden soil?
A: Dangerous could mean a lot of things, but usually when gardeners want their soil tested for dangerous soil contaminants, they are worried about heavy metals, like lead (Pb), cadmium (Cd), or arsenic (As), that could adversely impact human health. Understanding the association between soil contaminate levels and human health is tricky business; soil chemistries are extremely complex and sometimes certain forms of contaminates are tied-up in the soil (not biologically available) and therefore not a great risk to your health. Other times, you need to take action to minimize your risk of exposure. If a contaminant is lurking in your soil, it had to get there somehow. Things like leaded paint (manufactured prior to 1978) flaking off and falling into garden soil or residual lead from leaded gasoline (gardens that drain run-off from roads built prior to 1970) would be good reasons to have your soil tested. Children are particularly at risk and may have increased exposure if they play outside and inhale contaminated dust through their noses. If you are worried about soil contamination, contact your local Extension office or health department; you may experience peace of mind by paying to have your soil tested for contaminants (www.usual.usu.edu). However, be careful interpreting results on your own. Soil contamination interpretations are very complicated so it makes sense to ask a soil scientist to look over your results to determine if you need to be concerned. Your local Extension office can help you with this! These fact sheets provide more information on soil contamination and possible contaminate sources.
- Cornell Waste Management Institute – “Sources and Impacts of Contaminants in Soils”
- Washington State University – “Gardening on Lead and Arsenic Contaminated Soils”
- University of Minnesota Extension – “Urban Gardens and Soil Contaminants- A Gardener’s Guide to Healthy Soil”
Happy soil testing and here’s to a great growing season!