Do-It-Yourself Soil pH Test

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As home gardeners, we're always told to test for our soil pH. It's not one of the more fun or interesting tasks of tending a garden, but it really is crucial. Plants can access nutrients from the soil only if the soil pH is within a certain range. If the soil is outside of that range, you can add all the fertilizer you want and it will never make it into your plants.

What Is Soil pH?

Technically, pH means "potential hydrogen," and it is a measure of how many hydrogen ions are in a substance. For a gardener's purpose, pH indicates how acidic (sour) or alkaline (sweet) something is. Tests for pH generally apply to soil, but the pH of the water used in a garden also affects the growth of plants.

The pH measurement is a logarithmic scale that goes from 1 to 14. Anything with a pH less than 7 is acidic; 7 is neutral; anything higher than 7 is alkaline. Because it is a logarithmic scale, each value increases by 10 times. For example, a pH of 8 is 10 times more alkaline than a pH of 7. ​

Pure water has a neutral pH of 7. Cow's milk is slightly acidic at 6.5. Both tomatoes and beer measure 4.5. Lemons are very acidic at 2.5, and stomach acid is 2.0. On the alkaline end, sodium bicarbonate (baking soda) measures 8.4, ammonia is about 11.1, and lime comes in at 12.

Being acidic or alkaline isn't necessarily bad; it all depends on what the substance is interacting with. While most plants can adapt to any soil pH in the neutral range of 6.0 to 7.5, some plants have distinct preferences. Your weeds can even give you a clue about your soil pH. Dandelions, wild strawberries, and plantain proliferate in acidic soil. Chickweed, Queen Anne's Lace, and chicory favor alkaline soil.

In the garden, there are times when you want a slightly off-kilter soil pH. Lilacs love alkaline soil, and blueberries absolutely need some acidity. You need to know what you will be growing before making changes to your soil. Then you need to know your soil pH. A simple DIY test is a good place to start.

Do-It-Yourself Soil pH Test

This test can tell you on which end of the soil pH scale your soil is leaning, but for an exact measurement, you will need to get a pH soil testing kit or send a soil sample to a lab for testing. You can purchase home testing kits at most garden centers and through local cooperative extension service offices. Extensions also do soil testing.

Testing for Alkalinity

  1. Take a soil sample from 4 to 6 inches below the surface of your garden. If you have a small garden, you can mix soil from three or four different samples taking in different areas. If you have a large or spread out garden, it is better to test several samples separately.
  2. Remove stones, sticks, or other foreign debris from the soil, and break up any large clumps.
  3. Put about 1 cup of soil into a clean glass container.
  4. Add enough water to turn the soil to mud.
  5. Add 1/2 cup of vinegar and stir slightly.

If the soil fizzes, foams, or bubbles, your soil is alkaline. If not, test it for acidity.

Testing for Acidity

  1. Take a soil sample from 4 to 6 inches below the surface of your garden. Do not try this second test on the soil you poured vinegar on.
  2. Remove stones, sticks, or other foreign debris from the soil, and break up any large clumps.
  3. Put about 1 cup of soil into a clean glass container.
  4. Add enough water to turn the soil to mud.
  5. Add a 1/2 cup of baking soda and stir.

If the soil fizzes, foams, or bubbles, your soil is acidic. If neither test produced much of an effect, your soil is probably in the neutral range.

In general, acidic soil is made neutral by adding lime; alkaline soil is corrected with sulfur. How much to add depends on the actual correction needed, so the more accurate the test the better.