Hydroponics pH: How the Water’s Acidity Level Can Drastically Impact Growth


Unlike typical gardening, hydroponics is the art of growing plants without soil.  When you strip away the soil and grow plants in water alone, then the water becomes even more important to the process.  One element of water, the hydroponics pH, helps the plants to access the nutrients in the water and is therefore of key importance to the process of hydroponics.



What exactly is hydroponics pH?

Hydroponics pH
Hydroponics pH, Source


Although hydroponics pH is one of those terms that new hydroponics fans might be mystified by, the term pH is really not that difficult to understand. Basically, (pun intended) it is the measure of the acidity of the water. pH stands for “potential hydrogen,” as hydrogen ions and hydroxide ions determine whether a solution is acidic or basic.



Why is it important?

The pH level in your hydroponics water is extremely important and is one of the most important reasons for hydroponic plant failure. Because there is no soil in a hydroponic system, your plants need to get the nutrients through the water. You, in good, faith, are offering the plants a nutrient-laden solution, but because of the pH level of the water, they might not be able to utilize these nutrients. In other words, at certain pH levels, the nutrients are just not available for the plants to absorb.


The sweet spot is a hydroponics pH measurement of 5.8-6.5, although every plant has a different preference. If you keep the pH levels balanced to the preference of your plants, the plants will be able to receive the appropriate amount of nutrients and will flourish. If the water is unbalanced, however, you will have trouble growing your plants at all.



What is the science behind pH levels?

As you may remember from your junior high science class, water is made up of hydrogen and oxygen atoms. There are two hydrogen atoms for every one oxygen atom. The perfect balance is a pH of 7, and that is when there is one hydrogen ion and one hydroxide ion. When nutrients are added to the water, the molecules break up and the solution will then lean toward the acidic or the basic.


3D Water-Molecule
Water Molecule, Source


How is pH measured?

Because there are millions of ions in any nutrient-water solution, measuring the individual ions is not practical. Instead, the concentration of ions is measured to determine if a solution is acidic or basic. This is done on a logarithmic scale.

pH-Chart, Source


Acidic water solutions have more hydrogen ions. These solutions are measured from 0-6.9 on the logarithmic scale. Again, this scale does not measure individual ions, but rather the concentration of the ions. If a solution has more hydroxide ions, it is considered basic and has a measurement of 7.1-14.



How can I check the pH levels?

There are several easy ways to measure the hydroponics pH levels in your water. Just like junior high science, the litmus paper test is an easy, cheap way to check. Just dip the litmus paper into the water, and match up the color of the paper to the chart provided to find out where your water pH level falls. The liquid test works in a similar way but you just add a drop of testing liquid to a cup of your solution. These results are more accurate than the paper test. More accurate than these is the electronic meter, which will display the number right on the screen. These need to be taken care of carefully, however, as they are very sensitive.



How can you manipulate pH in a solution?

Understandably, anything you add to the water solution will affect the pH balance. In general, the nutrients themselves will make the water more acidic. Adding pH Up or pH Down to your water solution will help you move the pH levels up or down. pH down is mostly phosphoric acid, and is healthy for plants and fish if you have an aquaponic system. These calibrating solutions are both very easy to use.



What does buffering capacity have to do with pH?

If you are trying to change the hydroponics pH level of your water solution as above, and it stubbornly resists the manipulation, this might mean that you have hard water. The carbonates in hard water make it less susceptible to your attempts to change it, which means it has a high buffering capacity, or ability to resist change. If this is the case, a reverse osmosis filter could help expunge the mineral content in your water, which will allow you to balance the pH levels more effectively.



How do plants absorb the nutrients?

The main macronutrients that plants need, which refer to nutrients plants need in large amounts, find it difficult to move in very high or very low pH environments. Because your plants need macronutrients in large amounts, you want to keep the pH levels in the middle so macronutrients can be absorbed. On the other end of the scale, micronutrients come to plants in smaller amounts and are so affected by high and low pH environments that they can become poisoned by the toxic levels. These also need a pH balanced closer to the middle to avoid toxicity.



What is the optimum pH for hydroponic plants?

The rule of thumb is that fruits and vegetables will grow at a pH of 5.8-6.5, every hydroponic fruit and vegetable appreciates a different pH level. The trick as a hydroponic gardener is to group together like-minded plants so that they have the best possibility of success. For instance, tomatoes, squash, melons, and beans all grow between 5.8-6 pH level, so you should be able to use the same nutrient solution for them. But blueberries, on the other hand, like a very acidic environment of 4-5. As for an alkaline environment, this is perfect for growing crops like kale, peas, and onions, which prefer the higher scale numbers of 6-7 pH.


Although you probably don’t spend much time thinking about the pH level of the water you drink, if you are a hydroponic gardener, the pH levels of the water you use in the nutrient solution are extremely important. They affect your plants’ ability to absorb the critical nutrients that they need. There are several easy ways to check the pH levels of your water so that you can control the balance, and ensure that your plants flourish.





I'm Grammy to my grandkids and most of the authors here. My gardening career started when I was a child digging and planting in my neighbors garden in Florida. As a teenager I worked on one of the first organic farms and learned the many benefits of organic farming. As a young Mom I started dabbling in hydroponics and became hooked! My family and I learned from research and "Hard school of Knocks " ways to improve our crop growing techniques which I am willing to share with you.