If you want to be a successful hydroponic gardener, you need to understand some of the technical aspects of hydroponic growing, such as what pH is and why it matters in hydroponics. pH is not a complicated concept, but getting the balance right for growing hydroponically can be tricky.
pH is a scale of measurement to detect the acidity or alkalinity of a solution. It is important in hydroponics because pH affects the availability of nutrients to plants. Plants have optimal pH ranges where they effectively absorb nutrients. pH levels outside this range are detrimental to the plant.
Understanding pH and how to control this parameter in your hydroponic system is important for your success in growing healthy, fruitful plants. We will explain the basics of pH, why it matters for hydroponics, and how to test and adjust the pH of your hydroponic system.
What Does pH Mean in Hydroponics?
The pH of any solution, including hydroponic nutrient solution, refers to its acidity or alkalinity. The pH unit scale runs from 0 to 14, with 7 being neutral pH in the middle of the scale. A solution with a pH registering below 7 is considered acidic, while a solution with a pH above 7 is considered alkaline.
Most of us remember the basics of the pH scale from our high school chemistry days, and it is not a difficult concept, but how does the pH fit into hydroponic growing?
Hydroponic growing uses nutrients dissolved in water to deliver food to the plants in the soilless system. When salts, minerals, and micronutrients are dissolved in water, it can alter the pH of the water.
Water coming out of your garden faucet may also have a non-neutral pH if there are many minerals, such as calcium, dissolved in the water.
Why You Need to Monitor the Change in pH Levels
It is important to monitor the change in pH levels of your nutrient solutions because pH affects the availability of nutrients to plants. The plants’ roots are better able to absorb nutrients within a certain pH range.
For most plants, the ideal pH range where nutrients are most available to plants is between a pH of 5.5 and 6.5. This range is a generalization, and certain plants have very specific pH ranges that optimize their nutrient uptake, growth rate, and yield.
The pH range of 5.5 to 6.5 is slightly on the acidic side of neutral on the pH scale, and deviations on both sides of this range can be problematic for your hydroponic system.
The table below is a representation of the pH scale with the general ideal pH range for plants for optimal nutrient uptake highlighted.
Why Is pH Level Important for Hydroponics?
A plant’s roots take up nutrients from the nutrient solution and transport them to the rest of the plant. The efficiency of this process depends on the pH level of the nutrient solution because it affects the way the roots absorb nutrients.
If the pH level is acidic or too low, nutrients will not be readily available for plants, and if the pH level is too high, nutrients can become chemically locked out, and the nutrient solution becomes toxic for the plants. Either extreme can result in stunted growth or even death.
What Happens If pH Is Too Low in Your Hydroponics?
The lower the pH value is, the more acidic the solution becomes. Once the pH of the nutrient solution drops below the optimal range, the plants begin to suffer in a more acidic environment.
If the pH drops below 5, microbial action at the root level ceases, which is a problem for some plants that rely on bacterial action to absorb certain nutrients.
Once the pH drops below 4.5, it is usually too acidic for most plants. At this pH level, nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur cannot be absorbed by the roots. The absorption of iron, manganese, boron, copper, and zinc diminishes at this level but does not stop completely.
Essentially, at a pH level below 5, the nutrients become “locked up” and unavailable to plants. This results in the plants suffering from nutrient deficiency symptoms because they cannot absorb the nutrients from the solution.
What Happens If pH Is Too High in Your Hydroponics?
If the pH in your nutrient solution begins to rise, making the solution more alkaline, it can be as devastating for your plants’ health as too much acidity.
Once the pH rises above a pH level of 7, the plants’ roots can no longer absorb nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur cannot be absorbed by the roots. The absorption of the micronutrients iron, manganese, boron, copper, and zinc also stops at this level.
At higher pH levels, generally above a pH of 7.2, the alkaline nutrient solution becomes toxic to plants.
The plants will develop symptoms of nutrient toxicity, which can come about very quickly, causing the death of the plants.
It is important to monitor and test the pH of your hydroponic system regularly and make pH adjustments as needed to keep it within the ideal growing range for your plants. Doing so will help ensure that your plants are getting the nutrients they need for optimal growth.
How Do You Measure pH in hydroponics?
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There are several testing methods to detect the pH of your hydroponic solution. You can use test strips, a digital meter, or an indicator solution.
Test trips are the cheapest method but also the least accurate. To use test strips, simply dip the strip into your solution and compare the color change to the chart included with the strips.
A digital pH meter for hydroponics will give you a more accurate reading, but it can be more expensive than test strips. Many EC/PPM digital meters come with a pH meter function as well, such as the AERO-GRO 5-in-1 TDS/pH Meter (Amazon).
However, if you already have an EC/PPM meter that does not include a pH meter function, you can purchase a dedicated pH meter, such as the Bluelab PENPH pH Pen (Amazon)
It is important to test the pH of your hydroponic solution regularly, as even small changes in pH can have a big impact on your plants. If the pH of your solution gets too high or too low, it can cause your plants to become stunted or even die.
By keeping an eye on the pH of your hydroponic solution and making adjustments as needed, you can ensure that your plants will be able to absorb sufficient nutrients to stay healthy and thrive.
What pH Levels Should You use in hydroponics?
Most plants prefer a slightly acidic hydroponic environment, with a pH between 5.5 and 6.5. However, some plants (such as tomatoes) prefer a more neutral pH of around 6.8.
It’s important to know the ideal pH level for hydroponics for the plants you’re growing so that you can adjust the pH of your system accordingly and grow plants together in the same hydroponics system that like a certain pH range.
Hydroponics pH Chart
The following table shows some of the ideal pH ranges for some common hydroponic crops.
| Crop | Ideal pH Range |
| Strawberries | |
| Tomatoes | 5.5 – 6.0 |
| Cucumbers | 5.8 – 6.0 |
| Kale | 5.5 – 6.5 |
| Lettuce | 5.5 – 6.5 |
| Beans | 6.0 |
| Spinach | 6.0 – 7.0 |
| Peas | 6.0 – 7.0 |
| Rosemary | 5.5 – 6.0 |
| Chilli (Capsicum) | 6.0 – 6.5 |
| Peppers | 5.0 – 6.5 |
| Oregano | 6.0 – 7.0 |
| Basil | 5.5 – 6.0 |
| Mint | 5.5 – 6.0 |
How Do You Adjust pH Levels in Hydroponics?
Once you know the current pH reading of your hydroponic system, you can adjust it up or down as needed. You can use several methods to adjust the pH, ranging from commercial products to general household ingredients.
Most serious hydroponic growers use a pH control kit to adjust the pH levels in their systems. This kit normally comes with a “pH Up” solution to raise the pH and a “pH Down” solution to lower the pH of the nutrient solution.
A pH control kit such as the Standard Hydroponics pH Up and Down Kit (Amazon) is suitable for adjusting your hydroponic system pH.
If you run out of pH adjusters, you can use household ingredients such as citric acid, white vinegar, or even lemon juice to lower the pH and sodium bicarbonate or baking soda to raise the pH.
Always be conservative in your adjustments and creep up to the desired pH level, testing with your pH meter after each adjustment. This will prevent over-shooting the mark and need to adjust the pH in the opposite direction.
Conclusion
pH levels in hydroponics can make or break your success as a hydroponic grower. Just like with any plant, the pH of your water and nutrient solution will affect how well your plants can uptake nutrients.
Monitoring pH levels and nutrient PPM/EC levels are foundational to success in your hydroponics growing venture!
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