How to Test and Correct for Low Substrate pH in Your Growing Media

How to Test and Correct for Low Substrate pH in Your Growing Media

rhp-substrates-root-problems-webIf you mix your own or purchase a pre-mixed substrate, it is recommended you determine the initial pH. In too many cases, growers end up discovering low substrate pH.

According to W. Garrett Owen in the Michigan State University Department of Horticulture, determining the substrate pH prior to sowing seeds, sticking cuttings, or transplanting liners may save your crop from low substrate-induced problems such as bronzing, purpling, or spotting of the leaves. Therefore, this production challenge warrants discussion and distribution of corrective procedures.


Before any pots or flats are filled, it is important to determine initial substrate pH regardless if you mix your own or purchase pre-mixed.

The best method to determine initial substrate pH on-site is by conducting the 1:2 dilution test. To perform this test, you first need to:
• Prepare your substrate sample.
• Collect a representative sample of the substrate you plan to test. Moisten the substrate, but be careful to not to add too much water. The substrate should form a ball when squeezed in your hand when making a fist. Very little water if any should drip from your fist.
• After moistening the substrate, place it in a plastic bag and seal
• Allow the lime to react for three to four days to ensure the best accuracy.

After the pH has had time to equilibrate, you are now ready to determine the initial pH of your substrate.

For a step-by-step guide on how to do this, along with a how-to video, check out this article from Owen on Michigan State University’s Extension website.