pH is the measure of acidity or alkalinity of an aqueous solution. If a solution is acidic then it has a pH in the range of 0 to 6.9. If a solution is alkaline then it has a pH in the range of 7.1 to 14. Pure water or deionised water is neutral at pH 7.0. The ideal pH for most hydroponic gardening applications is between 5.8 and 6.2, except for Rockwool cultivation, which likes a slightly lower pH of about 5.5.
Why is pH important?
pH is the measure of acidity or alkalinity of an aqueous solution. The term pH refers to the potential hydrogen/hydroxyl ion content of a solution. Solutions ionise into positive and negative ions. If a solution has more hydrogen (positive) ions than hydroxyl (negative) ions then it is acidic and has a pH in the range of 0 to 6.9. Alternatively, if a solution has more hydroxyl (negative) ions than hydrogen (positive) ions then it is alkaline with a pH in the range of 7.1 to 14. Pure water and deionised water has a balance of hydrogen (H+) and hydroxyl (OH-) ions and is therefore pH neutral (pH 7).
If the pH of a solution is not within the correct range the plant will not have the ability to absorb some of the essential elements required for proper plant growth. All plants have a particular pH range, which will produce healthy growth, and this level will vary from plant to plant, but most plants prefer a slightly acidic growing environment (5.8 to 6.2), although most plants can survive in an environment with pH values between 5.0 and 7.0.
Plants grown in acidic environments can experience a variety of symptoms, including aluminium (Al), hydrogen (H), and/or manganese (Mn) toxicity, as well as nutrient deficiencies of calcium (Ca) and magnesium (Mg).
Conversely, in alkaline environments molybdenum (Mo) and macronutrients (except for phosphorus) availability increases, but phosphorus (P), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and cobalt (Co) levels are reduced and may adversely affect plant growth. From the chart you can see that each element can become more and less available to the plants as pH changes. If the pH of your solution is out of the desired range, one or more of the essential elements will become unavailable to the plant, causing nutrient deficiencies, which will result in slow growth rates and poor yields.