Why Your Soil Test May Mislead You

Should I get a soil test?  How can I build my soil?  

These are common questions that we receive at the farm.  Soil health is intriguing to me, and a topic of utmost importance to urban farmers and gardeners.  I recently watched “The Roots of Your Profits” with soil expert Dr. Elaine Ingham, in which she teaches about soil health at the Oxford Real Farming Conference earlier this year. It was absolutely fascinating!

I learned something interesting from her talk.  People often ask me if they should get a soil test. My reply is usually to suggest skipping the test and focusing on adding organic matter to the garden.  I always thought that this practice would balance the nutrients in the soil.  While my advice was correct, my reasoning was WRONG!

What do soil tests measure?
Dr. Ingham explains that soils contain the nutrients that plants need, but they are often in organic forms that are not available to plants. The nutrients are essentially locked up in the mineral content of the dirt.

Soil tests generally ONLY test for nutrients that are available to plants, and do not report the total nutrient levels locked in the soil.  By adding organic matter to the soil, we are not balancing nutrients, but UNLOCKING them!  Organic materials contain, attract and support soil microbes and fungi, which are the mechanism that releases the locked nutrients, converting them into forms that plants can use. 

A better test:
​If you are still curious about nutrient levels in your garden, a better indicator might be a plant tissue test, which measures nutrient levels in leaves.  This will show how much nutrient your plants have been able to uptake from the soil.  If the nutrients found in the leaves of your plants are at proper levels, you can be certain that your soil food web is working, unlocking and releasing nutrients and making them available to your vegetables.

What I do to build soil at the farm:
I personally do not test my garden soil.  It is expensive to do.  And no matter what the results may show, the ‘fix’ is almost always to add organic matter.  Compost, manures, green waste, cover crops and other natural soil amendments balance soil pH, improve soil texture, and attract the microbes that are necessary to release the nutrients that are already there, locked in the minerals and waiting to be released to feed your plants.

More Resources

  • I wrote an article that explains specific methods that you can use to build soil in your garden.  Read it here.
  • Watch Dr. Elaine Ingham’s Life in the Soil video series on YouTube: