Hydroponics and pH Basics

Happy New Year! and Happy Birthday P.J.!

The pH is very important in hydroponic gardening.   I will talk about some specifics of measuing pH in a later post.  The pH is measured on a scale of 1-14 with 7.0 being neutral. Acids are lower than 7 and bases (alkalinity) are above 7.
In order to understand how nutrients affect pH you should know the term pH is a measure of the hydrogen-hydroxyl ion content of a solution. These are the two components if you break apart water H2O (H+ and OH-). Pure water has an equal balance of hydrogen (H+) and hydroxyl (OH-) ions and is therefore pH neutral (pH 7.0). {Substances (molecules or atoms) with a charge are either positive or negative and are termed ions}. Since distilled water is pure water it has a pH of 7.0.  This is too high a pH for mos plants so I don't recomend using it without adding nutrients. When you add nutrients to water it can have a pH either higher or lower than 7.  If the solution has more hydrogen (positive) ions than hydroxyl (negative) ions then it is an acid (less than 7.0 on the pH scale). Conversely if the solution has more hydroxyl ions than hydrogen it is alkaline (or a base), with a pH greater than 7.0
When the pH is not at the proper level the plant will lose its ability to absorb some of the essential elements required for good growth. This depends on the plant and the nutrient. Some plants need a high amount of iron, and since iron becomes increasingly unavailable to plants as the pH approaches 8.0, these iron needing plants do poorly in basic mediums. For all plants there is a particular pH level that will produce optimum results, good growers experiment until they find their best or optimal pH for their plant(s). This pH level will vary from plant to plant, but in general most plants prefer a slightly acid growing environment (between 5.5-6.5), although most plants can still survive in an environment with a pH of between 5.0 and 7.5.
When pH rises 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. If you notice residue or salts in your reservoir when you change the water, you might want to adjust your pH down a bit. To use iron as an example again… Iron will be about half precipitated at the pH level of 7.3 and at about 8.0 there is virtually no iron left in solution at all. In order for your plants to use the nutrients they must be dissolved in the solution. Once the nutrients have precipitated out of solution your plants can no longer absorb them and will suffer deficiency and death if the pH is left uncorrected.
Not all nutrients will affect the pH the same! In other words you can manipulate the pH with the nutrients you add. Good growers will know nitrogen (an element required in large quantities for healthy plant growth) may be supplied in two forms (ammonium - NH4+ or nitrate - NO3-). These two forms of nitrogen when added to the nutrient solution  will result in different changes can result in large pH changes.
More on pH to come...
Good Growing,
Dr. E.R. Myers