The ABCs of Soil Testing

If you want to diagnose a plant issue, improve flower and vegetable production, or just understand what kind of soil you've got, it's time to do some testing. Soil tests can shed light on your soil's deficiencies and clue you in on which amendments you should add for better balance. Understanding your soil composition—beyond whether it is sandy, loam, or full of clay—is key to knowing which plants are going to grow well in your garden. I like the Rapitest kit from Luster Leaf. It's easy to use and reasonably priced.


What am I testing for?

A basic soil test can impart a lot of information:

  • Ph level: Acidity vs. alkalinity can determine which plants can thrive in your soil.

  • Nitrogen: Responsible for lush leafy greens and foliage.

  • Phosphorous: Helps plants grow roots, seeds, and flowers. It also fights off disease.

  • Potash (i.e., potassium): Strengthens a plants stems and helps with rapid growth.

Your test results will tell you which minerals you have in abundance and which you need to augment with certain types of fertilizers and feeds or with soil amendments, like garden lime and soil acidifier. Pay attention to the numbers associated with "N" (nitrogen), "P"(phosphorous), and "K" (potash) on a bag of fertilizer. If you your phosphorous levels are too low, you'll want a fertilizer that has a higher "P" number.


Performing a Soil Test

I wanted to get a better grip on the soil composition here at Greenleaf Garden so I tested a sample taken from the backyard.

After mixing the soil with water per the tests directions, I gave our heavy, red clay about 5 hours to settle.
After mixing the soil with water per the tests directions, I gave our heavy, red clay about five hours to settle.

I was pretty sure our soil was acidic and the test confirmed that with a pH reading of 6.0.

From left, our soil pH is acidic, our nitrogen levels are very low, and our phosphorous and potash levels are adequate.
From left, our soil pH is acidic, our nitrogen levels are very low, and our phosphorous and potash levels are adequate.

It was exciting to see that our potash and phosphorus levels are adequate. I was fascinated, although not surprised, that our nitrogen levels appear somewhere in the range of deficient to depleted. (The brown color of the water in our soil test, pictured above with the spade, is from unsettled clay silt; almost none of the purple tint we should have seen for nitrogen presence was visible.) We've recently noticed some slight yellowing of our lawn, another sign of a nitrogen deficiency, so our suspicions were confirmed.


Now that we've got a clear understanding of our soil's pros and cons, we can make more informed decisions about how to select new plants and how to care for what we've already planted. We'll definitely be applying a slow-release nitrogen-rich fertilizer to the lawn to help give it a boost.