Testing for pH

 

pH reading in Dave’s 
Potting mix with biochar

Why are we so hung up on pH?  To find out why, read “pH—What is it and Why is it Important” under Gardening Resources in the left sidebar.  It is one of the main keys to healthy flourishing plants.  

A question arises – should all pH testing be done at certified labs or is testing with on-site testing devices sufficient.

The sources we have consulted indicate that most commercial on-site probe-type testing devices are quite accurate, particularly if calibrated with a calibrating solution which has a known pH level. Many of the relatively inexpensive testing devices measure additional elements such as soil temperature, moisture level, etc.

A laboratory soil test should still be done every two or three years to compare to on-site tests, and to gain information about nutrients in the soil.  

Preparation for a lab test involves taking soil from multiple locations in the garden or a designated area of the garden to give a general overview or average reading for the tested environment.  The handheld testing instrument tests only in the specific location where the probe is inserted and in order to get a more generalized reading, you would have to test multiple sites with the results being averaged or accumulated in some way to give a general reading. 

VegHead Dave Skinner is one of our gardeners who routinely uses an on-site soil testing device with his greenhouse and potted plants and in his garden. Dave reports he has a good pH meter which measures the soil temperature and adjusts the reading accordingly. When we pulled the samples for lab testing from the VegHeadz beds this fall, Dave also tested them with his pH meter. His readings were considerably lower than the results we got back from the lab. Since then, he has recalibrated his meter to 7.0 using a buffering agent. He got very little change when recalibrating, so we believe his readings to be accurate.

He regularly tests the soil in his container plants and in his garden bed at home. Since he started adding biochar to his container mix, he has also tested and did not see any appreciable change in the pH at biochar concentrations of about 10-20%.

pH reading in Dave’s compost
with biochar added

He just recently tested again in both the completed potting soil with biochar and his compost bin with biochar and furnished photos of the results. The pH in the potting soil reads at 6.8 and in the unfinished compost, it reads 6.5. You can see the chunks of biochar in the compost photo because it has not yet been screened. The potting mix above has smaller biochar chunks that have passed through his quarter-inch screen. In both cases the biochar has been in the mixes for about a month and has had enough time to cause any pH change that might occur.

As a result, Dave has some doubts about the accuracy of the lab test results we are getting back for the VegHeads samples, which have consistently tested higher. We had tests done at a second lab to check the level of copper in the soil, but unfortunately, the alternative testing did not report back on the pH level so we could compare. 

It is possible that other biochar products which use a different source material might have a different effect on pH.

It will be interesting to see how this plays out in the VegHeadz garden as we begin to use biochar. Dave and the rest of us will be following the results closely. We will be posting updates as we learn more about how to use biochar and its effect on our plants.

How to calibrate a pH meter:  https://atlas-scientific.com/blog/how-to-calibrate-ph-meter/?srsltid=AfmBOoqa7lasc6EKbLHqQDMoNC-PfDh5Ir4DNodbeQ3AJuy2Yi0f6ZlP

https://edis.ifas.ufl.edu/publication/SS118