Hydroponics – All about pH

pH or the relative degree of acidity or alkalinity, is a vital component of a plant’s environment as the pH changes the ability of the roots to absorb nutrients changes. However, in order to understand pH and what to do with it, it is helpful to have some elementary knowledge of chemistry.

pH is a measure of the relative concentration of hydrogen ions or hydroxyl ions. They are called ‘ions’ because they are electrically charged. Hydrogen ions are positively charged while hydroxyl ions are negatively charged.

The standard pH scale runs from 1-14. Numbers below 7 and nearer the 1 are more acidic (relatively more hydrogen ions), those higher than 7 and toward 14 are more basic or alkaline (more hydroxyl ions). Exactly 7 is neutral, no ions or a balance between acid and basic. Any free hydrogen (H) and hydroxyl ions (OH) will tend to combine to form water, H2O.

Hydroponically grown plants will do well in a near-neutral environment and most plants thrive in slightly acidic conditions of 6.0-6.5. Apart from the chemical state in the roots themselves, nutrient solutions need to be fully dissolved into the growing medium (often water), so that they are more easily absorbed. A highly acidic or basic environment interferes with that. However, with easy to use kits it is now relatively simple to control the pH level. There are different types of kits but two of the most common kits include a bottle of solution and a container of powder respectively – each of these has good points and bad points.

With dry powder kits you need to make up a solution before you can feed the plants; the powder is concentrated but the setup is best when the material is in liquid form – if it is not sufficiently dissolved then inevitably the application is uneven. On the plus side powder kits are cheaper than solutions; they store well and providing they are kept sealed; the material will last a long time.

Solution kits may cost a bit more, but they are ultra-easy to use. You just measure out the exact amount, which is a little easier with solution than powder, and dilute or apply it as it is. Kits vary; many are highly concentrated solutions while others are premixed at the right concentration in the bottle. Before you can judge how much of a solution you should apply you first need to know what the plant’s environment is at that time. This is made easier with a pH testing kit.

Older testing methods are still available and often consist of simple colored strips. The paper strip is dipped into the plant’s medium and an embedded dye makes the strip change color – the color is then compared to a chart to gauge the pH level.

By contemporary standards this is a fairly inaccurate way to judge pH; as you can imagine. Today digital meters are the most popular means and these are generally more reliable than the strips. They do, however, need to be cleaned between tests to maintain accuracy whereas the paper strips can simply be thrown away.

Whatever kit and testing method you choose, it is essential to keep the plants’ pH near optimal levels. The difference between 6.0 and 5.0 in a pH level represents ten-times the difference in the concentration of acid present – and with pH levels, small numeric differences matter.