Why Should You Test Your Garden Soil pH?

Importance of Testing Garden Soil pH

What Is pH Lockout?

For example I was working with a gardener trying to resurrect a dying peach tree which was showing yellowing leaves (chlorosis) due to an iron deficiency.

The gardener applied chelated iron to the tree, figuring that would help correct the problem.

After I ran a soil pH test, however, I found that the peach tree was standing in extremely alkaline soil with a pH above a 9.0

Iron is completely locked out of most plants when the pH rises too high. For peach trees, iron lockout begins at a pH of 7.0 and above. Clearly, the 9.0 pH would not allow any iron absorption at all.

As expected, the application of iron did nothing for the peach tree.

An application of soil sulfur, however, helped to drop the pH down to an acceptable level along with some heavy soil-building techniques to improve organic matter content and soil quality.

After this, the chlorosis began to fade and the peach tree started to look a whole lot better.

This is just one example of pH lockout, but it's a very common issue especially here in the Sonoran Desert where native soil is far too alkaline to grow most vegetables in without some soil-building work.

How to Test Your Garden pH

Grab yourself a pH test kit or a pH tester pen. These are inexpensive, and are sold online, at your local hydro shop, or possibly even at garden centers.

You'll also need some pure distilled water, OR some water that's been adjusted to an exactly neutral 7.0 pH. Grab a jug of distilled water at the grocery store.

The only other thing you need for a soil pH test is any small container which you can add a pinch of soil and a few ounces of water to. Any small jar or cup will work:

Grab a pinch of dirt to sample. This may be from your garden, your native soil, your potting mix, seed-starting mix, or compost.

Consider here that the depth of your soil sample does matter. Sample soil at multiple different depths to gain a better understanding of your garden and how your amendments are affecting it.

Once you've got your sample(s), put one in the jar - it doesn't have to be full, just as long as you've got enough to get a good test on.

Add your distilled water, and shake it up so you've got some nice watery mud you can test.

Then grab your digital pH meter and give it a good reading, being sure to wait at least 30 seconds, or until the pH number stops changing. Be patient here until you've got an accurate reading.

What Does Garden Soil pH Indicate About Garden Health?

A healthy soil microbiome will be able to automatically maintain a pH that is close to ideal. If your pH is very far from the ~6.5 required for veggies, you've got some work to do on your dirt.

For instance, here in Tucson our native soil often has a pH of 9.0+ (crazy, I know!) and is extremely alkaline. Most plants which are not adapted to the desert here are unable to tolerate such levels and will suffer from severe nutrient lockout without adjusting the soil pH.

As you build healthy soil, though, the alkalinity of the native soil is tempered by a thriving microbiome and increased organic matter. Building healthy soil alone is enough to drop the alkalinity of native desert soil tremendously. It may not end up exactly in the ideal ~6.5pH zone, but will come far closer than 9.0+ after some time spent building soil and adding organic matter.

I still supplement with some soil sulfur twice a year, but my thriving microbiome does most of the pH adjusting automatically.

I know that if I test my soil pH and see a number that's too high, this is an indication that I need to do more work on building healthy soil, and that my soil has too much low-quality native alkaline dirt in it which needs to be diluted with more rich organic matter.