What is pH?

First, it is important to understand the basics of what pH is and why it is important. pH stands for power of Hydrogen or potential Hydrogen. It measures acidity and alkalinity by calculating the concentration of hydrogen ions in a solution. The pH scale ranges from 1 to 14. One to 6.9 is acidic, 7 is neutral, and 7.1 to 14 is alkaline. The scale is logarithmic, not linear, which means that pH 6 is 10x more acidic than pH 7, and 100x more acidic than pH 8. This is important to understand as a gardener.

How pH Can Affect Your Hydroponics System

pH is important to your garden because it will determine the availability and absorption of different nutrients. In general, a pH below 6 will reduce the absorption of phosphorous, calcium and magnesium, while a pH above 7.5 will reduce the availability of iron, manganese, copper, zinc and boron. A low pH of 3 to 5 is usually an indicator of fungal disease and creates an environment that will accelerate the disease.

To maintain a healthy garden, pH levels will need to be checked on a regular basis. The ideal pH range for soil gardens is between 6 and 7, while hydroponic gardens do better between 5.5 and 6.2. Soil is more forgiving than hydro, as there are natural buffers in the soil that help adjust the pH to healthy levels. Hydroponic gardens are more sensitive to pH because they don’t have the soil micro-organisms to help them out.

To check the pH of your nutrient solution, use pH test strips, drops or a meter. While the strips and drops will do the job, a meter will be the most accurate. Be sure to take care of your meter and calibrate it regularly so it always gives an accurate measurement. If you need to adjust the pH, use pH Up or pH Down solutions. Store-bought solutions are recommended, however, lemon juice as a pH Down and baking soda as a pH Up can be used in a pinch.

Causes of pH Swings and How to Fix Them

It is normal for pH to fluctuate slightly as plants feed. If you monitor the pH and EC, you will have a better understanding of what is going on with your plants. For example, if the pH increases and the EC decreases, this indicates the plants are feeding and it may even be okay to increase the nutrients you are giving them. If the pH decreases and the EC increases, this means you are probably overfeeding your plants and they are putting nutrients back into the water, so feed them a little less. If the pH and EC remain stable, then you are achieving maximum growth because your plants are taking in equal parts nutrients and water.

You’ll obviously want to strive for equilibrium and maximum growth, however, it is better to underfeed just a little and allow for a natural pH swing than to overfeed. Many hydro growers will allow for a swing from 5.5 to 6.2. They will feed at 5.5 and when the nutrient solution reaches 6.2 they will make new solution. One benefit to this method is that plants are better able to uptake nutrients at different pH levels, and by going through a range of pH levels, your plants will have better access to different nutrients, resulting in more optimal growth.

If your solution’s pH rises or drops dramatically within a day or two, then you may have another issue you need to address. There are a few possible reasons this may be happening.

The Medium

The first thing you’ll want to check is your medium. Some mediums have buffers that naturally adjust the pH back to their preset levels. These mediums need to be cleaned and pH-adjusted before you use them. For example, stonewool has a naturally high pH, so you must soak it in a solution of pH 5.5 before using it. Sphagnum peat moss generally needs limestone added to it to bring it down to the plant-friendly zone of 5.5-5.8.

Bacteria and Algae Growth in System

Another common cause of dramatic pH swings is bacterial growth in your reservoir. When organic matter is present, such as rotting roots or media that isn’t fully composted, the bacteria that decomposes the matter will release organic acids, which lowers pH. If your pH drops to 3 to 5, this more than likely indicates root rot. If the root rot is in its beginning stages, you may be able to treat the roots with hydrogen peroxide. If this doesn’t work, you will want to remove the dead roots from your plants and cross your fingers they bounce back.

If light is somehow getting into your reservoir or hydroponic system, you may have algae growth, which raises pH levels. Algae needs light to grow, so by simply shading your reservoir and plant sites, you can prevent algae growth in your system. There are products at your local hydro store that can rid your system of existing algae.

Your Water

The water you use might be the culprit of your pH woes. The quality of water varies from region to region, and changes with the weather. Different regions have different minerals present in their soil and water, some of which could act as buffers that naturally adjust the pH of your solution. Heavy rains may alter the composition of your water as well. City water might contain added chemicals to clean the water. This is why you will see hard water versions of nutrients at your hydro store. If you are having pH issues you can’t seem to solve, you may want to invest in a reverse osmosis water filter to give your water a clean slate.

If you are growing in a hydroponic system, the volume of water you are using could also be the cause of a pH swing. If you are using less than 1 gal. of water per plant, this is more than likely the issue, as your plants will eat up the nutrients quickly, resulting in a higher pH in a short amount of time. An average size plant needs 1-1.5 gal. of water, whereas a large plant needs up to 2.5 gal.

pH plays a critical role in your garden. Be diligent about checking your pH levels and quick to correct any issues that pop up. By learning how the different components of your garden affect the overall chemistry of your system, you will be better prepared to solve issues as they come.