This article deals with the pH of hydroponic gardening and the availability of nutrients at different pH levels in a soiless growing medium. Organic and dirt gardening have different levels, so the following chart doesn't pertain to them. To be technical, the term pH refers to the potential hydrogen-hydroxyl ion content of a solution.
Solutions ionize into positive and negative ions.
When the water is less than pure it can have a pH either higher or lower than 7. When the pH is not at the proper level the plant will lose it's ability to absorb some of the essential elements required for healthy growth. When pH raises above 6.5 some of the nutrients and micro-nutrients begin to precipitate out of solution and can stick to the walls of the reservoir and growing chambers. In order for your plants to use the nutrients they must be dissolved in the solution. Some nutrients will precipitate out of solution when the pH drops also.