One of the most overlooked, but important, factors of growing healthy plants is pH. In hydroponics it is necessary to monitor pH levels because pH effects the solubility and uptake of essential plant nutrients. During different phases of a plant’s life cycle some minerals will be used in greater quantities than others. When the mineral levels change, so does the pH. Accurate measurement and adjustment of the pH based on the growth cycle of the plant is a critical element in Hydroponics.

PH is the measure of the acidity or alkalinity of the solution. A neutral solution has a pH of 7. Higher than 7 is considered ‘alkaline; and lower than 7 is considered ‘acidic’. Pure water has a pH of around 7. Most flowers and vegetables flourish within a range of 5.8 to 6.8. However, a pH of 5.8 – 6.3 is considered ideal for most hydroponic plants. See our Vegetable pH/PPM/CF Chart for more information.

What pH should I maintain?

Recirculating: 6.0 – 6.6

Run-to-waste: 5.5 – 5.8

During the last three weeks of the flower stage, run your pH at 6.2 – 6.8. This will make P/K more available to the plants. Our favourite PK products are Frooting Power and BAC F1 Booster.  

How do I Measure pH?

Use a pH pen, digital waterproof pH meter, or even a simple pH test kit to measure pH levels. You may also need pH(up) and pH(down) to adjust the pH of the nutrient solution.

Problems Caused by Incorrect PH

If your pH levels drift outside of this range, your plant will not be able to uptake certain nutrients. This can cause nutrient deficiency or toxicity. Additionally, certain nutrients, such as calcium, may solidify and fall out of the solution. This is known as scale, a white substance that you may have seen on the walls of your reservoir. The following chart illustrates the pH levels at which certain nutrients are best absorbed by plants.

The chart illustrates that a nutrient such as Nitrogen can be absorbed within a wide pH range (5.0 – 9.0), whereas Phosphorus can only be absorbed from pH 5.0 – 6.0 and 9.0 – 10. Because most nutrients are best absorbed within the pH 5.5 – 6.0 levels, that is considered the optimal range for plants.