Terry Strecker

Imagine if coffee mate and sugar never dissolved in your coffee. Or cream and sugar never dissolved in your tea. Plants face a similar dilemma when they are grown in soil with the wrong pH. Soil pH is responsible for the ability of 16 plant nutrients to dissolve in ground water. Plants can absorb only dissolved nutrients through their roots.

Every Spring in East Texas, beautifully blooming azaleas are an example of the plant’s need for the correct soil pH. Azaleas thrive in acidic soil, that being soil with a pH below 6.0. Why? Because azaleas need the form of iron that can dissolve in acidic soil. For East Texas gardeners, soil pH is a key factor in achieving success with certain plants, such as azaleas, blueberries and hydrangeas.

What is soil pH and why is it so important? The term “pH” is a chemical measure of how acidic or alkaline a soil is. Acidic substances, such as lemon juice (“sour” or “tart”) have a pH below 7, while pure water has a “neutral” pH of 7, half way between the extremes of 0 (extreme acid) and 14 (extreme alkaline) on the pH scale. An alkaline solution of bleach will have a pH well above 7. While pH 6.0-7.5 is acceptable for most plants since most nutrients dissolve in this range, acidic soil (pH below 6.0) can give certain plants a nutrient advantage.

Some nutrients dissolve more readily in acidic soil pH, such as iron (Fe), which is an essential plant nutrient. The most abundant form of iron is Ferric Oxide (Fe2O3) which gives soil a red color. Unfortunately, Ferric Oxide is not very soluble in ground water. Thankfully in East Texas, as the soil pH decreases, the level of water-soluble Ferric Hydroxide (FeHO2) increases. So, although we live on a natural layer of insoluble Ferric Oxide (Fe2O3), the acidic soil in East Texas changes insoluble Ferric Oxide into soluble Ferric Hydroxide (FeHO2). Hurray! The acidic soil in East Texas changes our natural iron resource, the poorly absorbed Fe3+ (Ferric Oxide), into the more water soluble Fe2+ (Ferric Hydroxide). As a result, plants, such as azaleas, have plenty of soluble iron to absorb from the ground water in East Texas acidic soil.

Given how important soil pH is to plants (azaleas, blueberries and hydrangeas, to name a few), get a soil test at https://soiltesting.tamu.edu/ described by Keith Hansen at https://agrilife.org/etg/2015/03/17/dont-guess-soil-test/. Not only will you find out your soil’s pH but the concentration of important nutrients in your soil.