Plants can only absorb hydroponic nutrients when the pH is within the ideal range, which is generally between 5.8-6.5. If your solution’s pH is not within this range, then your plants will be unable to absorb enough nutrients which will impair them in carrying out all the necessary processes that allow them to thrive in otherwise ideal conditions.
Fear not, however, as we will look at what pH your hydroponic system needs and how you can properly monitor and maintain its levels through accurate use of nutrient feed.
Importance of pH Level
The pH scale ranges from 0 to 14, with 0 being the most acidic, 14 being the most alkaline and 7 being the pH-neutral point. All plants are different, however, and some prefer acidic conditions while others may require an alkaline environment.
A pH that is too high/alkaline can prevent nutrient uptake and lead to deficiencies. Iron deficiency causes pale or yellow leaves in young plants, while leaf cupping and tip burn are both signs of calcium deficiency. Calcium also tends to form salts that leave white deposits or scale on your reservoir walls and equipment, which in turn can cause blockages and poor water circulation through your system.
Firstly, you should always use a feed specifically tailored for hydroponic systems because plants grown via hydroponics require different pH levels than grown in soil. Soil already has plenty of beneficial microorganisms and organic matter to help your plants grow. Its naturally rich makeup also allows for interactions between water and minerals that can help regulate pH levels. Without this you must be vigilant and thorough, constantly monitoring and adjusting pH levels. There are of course some exceptions, however, the optimal pH range for hydroponically grown crops sits in the near-neutral range between 5.5-6. Many fruits and vegetables, such as melons, apples, beans, squash, and tomatoes prefer that range. Some fruits and vegetables have a wider optimal pH range, such as pumpkin which requires a pH between 5.5-7.5. Likewise, other crops like things a bit more alkaline including kale, onions, and peas, which prefer levels between 6.0-7. Mint likes it super alkaline at 7.0- 8.0.
Hydroponic Nutrients and pH Range for Plant Uptake
Hydroponic nutrient product ranges typically start with pH levels between 5.5-6.0 but can vary depending on their individual formulation. For example, ammonium nitrate is more acidic than nitrate and will cause a drop in pH (more acid). Calcium salts, on the other hand, can cause a rise in pH (more alkaline). Each nutrient is unique and requires certain pH levels to make for efficient plant uptake. The wrong pH level can result in too little or too much of a certain nutrient being taken up by the plant. For example, when the pH level drops below 5.0, plants can stop or “lock out” any update of magnesium and calcium resulting in deficiencies, while in contrast, it can cause copper and iron toxicity as these nutrients thrive at a slightly lower pH. A pH level that exceeds 6 or 6.5 can also induce an iron deficiency.
It's important to monitor nutrient solution levels by testing pH and EC.
Why pH Levels Fluctuate in Hydroponic Systems
There are several reasons why you could see pH levels fluctuating within your hydroponic systems. One of these is because plants can absorb more water than nutrients if needed, which can then cause massively varying pH levels. It is therefore important to monitor nutrient solution levels by testing pH and EC. You should keep the reservoir full by replacing it with a fresh feed when pH levels are too far out of range. Do not just top up the reservoir in this scenario as the solution that is left has a higher pH and will increase the strength of the new feed you add, meaning you are back to square one.
Both inorganic and organic matter can affect pH levels in hydroponics systems. To get an accurate pH reading in a media-based system, test the pH of the reservoir solution as well as the run-off draining from the pots, beds, or bags holding the plants.
Algae and bacteria are the main types of organic matter that affect pH levels in a hydroponic system. If pH levels rise in the morning and drop later in the day, algae may be the culprit. As algae consume acidic carbon dioxide during the day, pH levels rise and then fall by evening. On the other hand, bacteria from root disease can cause a dramatic drop in pH levels. As diseased roots decompose, bacteria will release acids into the hydroponic solution.
The first and most important factor in maintaining liquid nutrient levels in hydroponics is constantly testing and monitoring pH levels. There are a variety of ways to do this including test strips and liquid test kits (that are the least expensive) as well as digital pH meters that are more expensive but provide accuracy and offer repeatable results. I would recommend testing your pH at least every other day or on a daily basis if you have recently adjusted nutrient levels or are just starting out in hydroponics.
If you are using a recirculating system you should adjust the pH level according to test results from the main reservoirs. In a media-based system, however, the pH will change as the nutrient solution travels through the system and out as “run-off.” Therefore, you should test and adjust your pH levels based on the pH of your run-off.
Products for Balancing pH
There are ready-made products you can buy to help correct any issues with incorrect pH including “pH up,” which is made up of phosphoric acid, and “pH down,” which is made up of potassium hydroxide. Be warned: it is easy to overdose with pH down and pH up and it is more damaging to add too much pH down or pH up than having solution that isn’t in the ideal range. For this reason, you should only use pH down or pH up very sparingly and adjust pH to your chosen level over the course of several days.
Be sure to only use a feed range suited for hydroponic growing. Organic elements that are contained in feed ranges designed for use with other mediums or systems can ferment when used in a hydro system, causing residue and algae that can damage your pH, plants, and equipment.
If you want to be as accurate as possible but don’t have the time to manually check your pH levels every day then you can purchase automatic pH controllers. These cost more than pH up or pH down products, but they will maintain your pH at a consistent level.
Automatic controllers are a great choice if you are using a re-circulating system where pH fluctuations regularly occur as your plants feed themselves repeatedly from the same solution.
The type of water that you use is important also. If your water is hard, the buffering effect from the high mineral levels will cause high pH levels. If this is the case, then a reverse osmosis system is an efficient and affordable method for reducing water hardness.
Reverse osmosis is the process where any contaminants or dissolved minerals that may cause water to be hard are removed by forcing the water through a filter.
Each type of plant needs certain growing conditions to thrive. It really is worth the time and effort to monitor and adjust pH levels in hydroponic systems. If you know the optimal pH ranges for your plants, you can take the necessary steps to keep your hydroponically grown plants in the best of health.
Read next: Automation Must-Haves for New Growers