Saturday, June 8, 2019

4 Thinks You Should Know About Soil pH

Soil samples with beakers

Plant descriptions often include brief statements about the acceptable range of soil pH for those particular plants to thrive. So, there are four things you must know about soil pH. They are:

  1. A low pH indicates an acidic environment,
  2. A high pH indicates an alkaline environment,
  3. pH of 7 is neutral, or right in the middle, and
  4. You can take a sample to the nearest Cooperative Extension Office for lab analysis to find out the pH of your soil.

That’s all you really need to know. As with most things in life, a little basic knowledge is enough for us to function. If you’re satisfied now, please go to, and check out my plants. If you’re curious and want to learn a little more, read on.

The meaning of p and H

Believe it or not, no one really knows for sure what “p” is supposed to mean! It depends on whose speculation you adopt. According to Wikipedia on pH (which is the obvious authoritative source for everything),

“The concept of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. In the first papers, the notation had the "H" as a subscript to the lowercase "p", as so: pH.

The exact meaning of the "p" in "pH" is disputed, but according to the Carlsberg Foundation, pH stands for "power of hydrogen". It has also been suggested that the "p" stands for the German Potenz (meaning "power"), others refer to French puissance (also meaning "power", based on the fact that the Carlsberg Laboratory was French-speaking). Another suggestion is that the "p" stands for the Latin terms pondus hydrogenii (quantity of hydrogen), potentia hydrogenii (capacity of hydrogen), or potential hydrogen. It is also suggested that Sørensen used the letters "p" and "q" (commonly paired letters in mathematics) simply to label the test solution (p) and the reference solution (q). Currently in chemistry, the p stands for "decimal cologarithm of", and is also used in the term pKa, used for acid dissociation constants.”

(If your eyes are now rolling back in your head, go to and check out the plants. If not, read on.)

As noted before, H means “Hydrogen”. That’s easy enough to understand. So, “pH” refers to the concentration of hydrogen ions on soil particles. More particularly, it refers to the quantitative relationship between hydrogen ions and hydroxide ions. (I’m not going to explain the difference.) The accepted scale of measurement ranges from 0 to 14, with 7 being neutral. Solutions with more hydrogen are lower on the scale, so are acidic. Hydroxide solutions are higher on the scale, so are caustic or alkaline.

Why soil pH matters to plants

Soil pH matters to plants because it affects the availability of soil nutrients to their roots. Their roots can only absorb nutrients in certain ionic forms, and this can only occur within certain pH ranges. If the pH range is wrong, the nutrients are not made available to the plants. Most of the plants that we grow in our gardens require a soil that is more or less acidic. So, plant descriptions tell us what pH range is acceptable to that particular plant. Thankfully, the acceptable pH range is usually fairly wide. You will find, however, that if the pH range creeps up or down, the plant will begin to suffer and show signs of stress.

How pH changes

pH changes due to environmental factors. It can happen by itself, or you can make it happen. A soil scientist advised me a long time ago to test my soil the same time every year because seasonal changes can affect pH. Though the changes might be minor, differences will show on the soil test results and influence the recommendations.

If you need to make it happen, you won’t know unless you take a soil sample to your friendly local Cooperative Extension Service for analysis and recommendations. If you’ve never had your soil tested, start by doing it annually. Learn what changes result over time. If you see the pH stabilizing at a proper level year after year, take samples less frequently. If you observe signs of stress – chlorosis, for example – have your soil tested at once.

When you collect your soil sample, follow the instructions provided. One such instruction will direct you take soil from more than one place in your garden, and mix it up so you have a general soil profile. When you receive the results, follow the instructions. (I don’t know why I feel like I have to keep saying so.)

Now, if you’ve read this far, you should check out the plants at Be sure to observe the soil pH recommendations.

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