Last time, when I wrote about soil texture, I mentioned that the easiest way to figure out the texture of your soil was to get it tested. Many – if not most, or maybe even all – of the land grand universities throughout the United States either house or are closely associated with a soil testing laboratory. So, as always, talk to your local extension agent about the details for the closest lab to you.
While an undergrad at Utah State University working on my horticulture degree, I worked part time at the USU Analytical Laboratory where we did testing on soil, manure (those were smelly days), plants, feed (also smelly days if the feed was silage), and water. Even though I did a lot of sample drying and grinding, I actually really loved that job. Besides the grinding, I also ran a lot of pH tests, organic matter tests, and potassium and phosphorous tests. I learned a lot about soils and had fun making up “mud-pies” for some of the tests.
If you’ve never had your soil tested, or if it’s been a few years, or if you’re having trouble with some of your plants, you should definitely consider sending in a sample to get tested. It’s fairly inexpensive – depending on the exact tests you want done – and you can get results in a couple of weeks that not only tell you about the soil you have, but also include recommendations on how to improve it.
It’s generally recommended that you collect soil from 5-20 different parts of your garden (the number of samples will be dependent on how big your garden is), combine it all together, and then send in a sub-sample to be tested. Keep in mind that if you’d like to see if there is a difference between the soil in your flower garden and your vegetable garden, and if these gardens are physically separated, you’ll want to keep the sampling separate also. So, you’d dig up soil from 5 or so random locations in your vegetable garden, mix that together, and then take a sub-sample out – make sure it’s labeled! – and then you’d do the same for your flower garden. For a routine analysis (which at the USUAL includes: texture by feel, pH, salinity, phosphorous and potassium) the amount of soil you need is only about two cups. If you want additional tests you might need a bit more, but as a general rule, 2 cups is fine.
At USUAL, when we’d receive a sample the first thing that would happen is we would set it out to air dry. After the sample was sufficiently dry, we’d have to grind it either by hand with a mortar and pestle, or with a machine if it was too clayey. Once it was all a fairly uniform size, and if we were performing a routine analysis, we’d use the majority of the sample for the pH and salinity tests. Leaving only a few tablespoons in the box, we’d use the rest to make a saturated paste (mud pies, basically) with the soil and some de-ionized water that we would then spread out in some leaching dishes. The liquid would drip through into some beakers, and it was this liquid that we would use to test for pH and salinity. Determining the texture would take up the next biggest amount of the sample, and with the remaining teaspoons (such a small amount, I know!, but that’s all that is needed) the other tests would be performed. I loved doing the phosphorous tests because the solution that we made would be a different shade of blue depending on how much phosphorous was present. The same happened with the organic matter, but instead of blue it was a range of oranges and reds. Lots of fun chemistry happening!
If chemistry isn’t your forte, and you’re not even sure what phosphorous is or does, no need to fear. Like I mentioned earlier, along with the results, you also get a brief explanation of those results as well as recommendations for your garden based on what your gardening goals are.
For more information on soil testing in your area, check out your local land grant university or talk to your local extension agent.