The pH of irrigation water is one of the most critical factors to consider if the goal is to achieve optimal utilization of applied nutrients and high-quality harvests.
What is pH?
pH stands for «Potential of Hydrogen» and is a measure used to determine the degree of alkalinity or acidity of a solution, as it indicates the concentration of hydrogen ions within the solution.
We talk about positively charged Hydrogen ions (H+)
Thus, pH is used to measure the acidity or basicity of a liquid substance or a dissolved solid. It has a measurement range spanning from 0.0 to 14.0, where substances with a pHbelow 7.0 are considered acidic solutions, substances with a pH above 7.0 are considered alkaline or basic solutions, and substances with a pH of 7.0—or close to it—are considered neutral solutions.
pH is like a thermometer that measures the temperature of a substance, where temperatures below 37°C are cold (acidic), temperatures above that are hot (alkaline), and those around 37°C are temperate (neutral).
The Importance of Measuring Water pH in Marijuana Cultivation
When cultivating cannabis systematically with the aim of producing a high-quality final product, it is important to monitor the pH levels of the irrigation water. This ensures that the supplied nutrients can be effectively absorbed by the plants—specifically, by their root systems. If pH levels fall outside the optimal range for nutrient availability, various nutritional problems will inevitably arise. These issues are often caused by the accumulation of minerals in the growing medium, which can create a toxic environment for the roots and even block other nutrients, preventing their proper absorption.
If fertilizers are to be added to the irrigation water, purified (bottled) water should be used. The final pH of the solution—after all fertilizers have been added—should be between 6.5 and 7.0; if it drops below this range, the solution becomes acidic, whereas if it rises above it, the solution becomes alkaline
Ideal pH values for growing marijuana in hydroponic or aeroponic systems, or in inert media:
Initial weeks of growth: pH 5.8 – 5.9
Pre- flowering stage: pH 6.0 – 6.2
Actual flowering stage: pH 6.0 – 6.3
Ideal pH values for growing marijuana in peat mixes or directly in soil:
Initial weeks of growth: pH 5.5 – 6.0
Pre-flowering stage: pH 6.0 – 6.2
Actual flowering stage: pH 6.2 – 6.5
Irrigation
When watering your plants—whether using plain water, water with additives, or a hydroponic system—I recommend the following:
Watering with plain water only
Let the water sit for a few minutes, insert the pH meter, and note the reading once it stabilizes. There are specific products available to adjust water pH; if you use them, be sure to follow the manufacturer’s instructions step-by-step.
Watering with additives
This process varies depending on the line of fertilizers used, as some manufacturers recommend measuring and adjusting the pH before adding the fertilizers, while others recommend doing so after dissolving them in the irrigation tank.
Dissolve the fertilizers one by one in the irrigation tank, stir to ensure a thorough mix, and let the solution rest for a couple of minutes to allow the pH to stabilize; only then you should measure the pH again to determine the mixture’s exact value.
I should add that if foam forms, you should let the mixture rest a bit longer, as the foam can interfere with the pH meter’s reading.
Irrigation in hydroponic systems
These systems typically use an irrigation reservoir paired with an automated watering setup, holding the water and nutrients the plants need for approximately one to two weeks. To regulate and maintain the pH level within the ideal range, you need pH and temperature monitors; you can then adjust the pH as necessary based on the readings.
Instrument for measuring pH
This is a basic pHmeter ideal to measuring hydrogen ion potential.
