Soil Sampling, Testing and Analysis: Soil Composition

Find Your Soil pH and Know what to Do with the Results

Soil cultivation

Testing your garden soil is a necessary step in determining what your plants will need to grow well and stay healthy.  Without a clear idea of your soil's make-up, you can throw all kinds of things into it, but they may not be the right things, or they may be completely unnecessary.  Think of it as trying to make your grandma's beef stew without a recipe - you can probably guess at some of the right ingredients, but without that recipe, it'll never turn out exactly the way you hope. Here's how to do a soil analysis.

  1. How often should you test your soil?  The obvious answer is, whenever you put in a new garden.  However, you may also want to conduct a soil test every five years or so, just as a precaution.  The balance of minerals in your soil will change as plants use up the supply of some minerals, and possibly add to the supply of others.  Another time that a soil test can be helpful is when your plants, or even your lawn, just isn't performing the way you think it should.  Although you can sometimes figure out what's wrong with your plants by the symptoms they exhibit, a soil test will give you a more definitive answer.  Soil testing will also tell you about the pH balance of your soil.  This can be useful if you're putting in plants which have definite preferences about what type of soil they're placed in.  For example, you'll never get the beautiful deep blue color for which hydrangeas are famous if you plant them in alkaline soil.
  2. What is the proper way to take a soil sample?  The first step is to learn how to obtain a soil sample properly.  You will need to remove any vegetation from the soil surface, such as grass, plants or mulch when soil sampling.  Next, use a spade, trowel, or soil auger to remove a plug of soil that is approximately six inches deep.  Place the soil sample in a clean bucket or plastic bag.  Repeat this process ten to fifteen times, depending on the size of the area you're sampling.  This helps to ensure that the sample is as representative as possible of the area that's being tested.  Do not obtain samples from areas that have already been chemically treated, because they will not accurately reflect the composition of your soil.
  3. Where do I submit the soil sample for testing?  Most university extension services offer soil testing or maintain a list of labs that do, so if you live in a state with an extension service, this is the best place to start.  If this isn't an option, or if you live outside of the United States, you can do a quick Google search for soil testing laboratories and the name of the state or territory in which you live.  It's a good idea to use a local soil testing lab if possible, because they will be more familiar with what the norm is for soil components in your part of the country.  Once you've found a soil testing lab, obtain a soil test kit.  This will usually consist of a container in which to place your soil sample, along with specific instructions on how it should be submitted.  When you send in your sample, be certain to thoroughly mix the various soil samples that you obtained.  There should be no large dirt clods, and the consistency of the soil should be relatively fine.
  4. What tests will be conducted?  The test will determine the level of the most important minerals present in your soil, which are phosphorus, potassium, calcium, magnesium, iron and zinc.  It will also determine the pH balance of your soil - a pH balance below 7 is considered acidic, and above 7 is considered alkaline.  This can be a huge money-saver because you can decide how much and what kind of fertilizer is right for your plant.  This is also a more environmentally-friendly way to apply fertilizers than just randomly dumping it into the soil at the recommended rate.
  5. After the test results are received, what comes next?  When you receive the results from your soil testing kits, you'll need to decide what is necessary to amend the soil.  If you are planting the aforementioned hydrangeas and the soil test shows that you have alkaline soil, you'll need to add a material such as peat moss, sulfur or ammonium sulfate.  This is especially important if your soil pH is above 8.0, because extremely alkaline soils prevent minerals from becoming available to plants.  You'll also need to decide on an appropriate fertilizer based on your test results.  If your test shows unusually low levels of potassium in your soil composition, you'll want to choose a fertilizer high in this mineral to compensate for it.

Once you've determined exactly what challenges you're up against, you can get to work creating the perfect soil quality - or at least, giving it your best shot!


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