Plants grow in a variety of climates and conditions including temperature ranges, altitude, soil composition and more. Today, we’ll be discussing another one of these conditions that can have a significant impact on plant growth and health – soil pH.

pH is the international symbol for the measure of aqueous solution. It stands for the “power of hydrogen” and measures how acid or alkaline the soil is. Without going too much into the science details, pH is measured on a scale from 1- 14, with 7 being neutral. Numbers below seven are considered acidic and numbers above seven are considered basic (also called alkaline). pH is measured on a logarithmic scale, meaning each change in pH value is an exponential increase rather than a linear increase.

When it comes to gardening, most vegetables and flowers prefer soil with a slightly acidic or neutral pH, in the 6.5 – 7 range. Some plants like blueberries prefer a much more acidic soil in the range of 4-5. Other plants like boxwood prefer a slightly alkaline soil in the range of 7 – 7.5.

Soil pH affects plant growth in a variety of ways. The primary way is the uptake of minerals and nutrients. Before the plants can absorb and utilize certain nutrients, it first must be dissolved in a solution. Certain minerals and nutrients are more soluble at certain pH levels, which means that even if there is an abundance of a certain mineral, if the pH isn’t suited to that mineral for it to dissolve and then be taken up by the plant, the plant could be suffering from a nutrient deficiency.

Soil pH can change as a result of of rainwater leaching away various elements (ex. calcium, magnesium) and also by the breakdown of organic matter to create acid compounds. It can also be changed by adding things like lime to raise soil pH and adding sulphur to lower soil pH.

To measure your pH, there are a number of commercial kits that can be purchased that include strips or devices, sending it off to a lab to be tested, and even a rough DIY method using baking soda and vinegar.

Cover Image by Tess Watson, used under its Creative Commons license.

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