pH Meter Calibration: Keep Your Marijuana Plants Happy

Although there are plenty of hardy cannabis strains out there, not learning the science of cultivation will prove costly down the line. There are plenty of considerations, including one that a high percentage of less-experienced growers seem to forget about: pH meter calibration.

It is an essential component of a successful marijuana grow, and this guide highlights everything you need to know about it. The good news is that the process is far easier than you might think.

What Is pH?

pH (potential of hydrogen) measures how basic or acidic a liquid solution is. The pH scale goes from 0 to 14. Pure water is deemed neutral and has a pH value of 7. If a substance has a pH below 7, it is considered acidic. Any substance with a pH above 7 is considered basic.


Battery acid is the most acidic substance, with a pH of 0. Meanwhile, liquid drain cleaner is the most basic substance, with a pH of 14. The pH scale is logarithmic, which means an increase/decrease in an integer value means a tenfold change in concentration.

For instance, lemon juice with a pH of 2 is ten times more acidic than orange juice with a pH of 3. Ammonia with a pH of 11 is ten times more basic than milk of magnesia with a pH of 10, and so on.

Why pH Matters in Marijuana Growing

pH impacts your marijuana plant’s ability to transport its own carbohydrates and nutrients. Different plants perform best within different pH zones, so it’s essential to know what to look for when cultivating weed.

For instance, the right range for cannabis cultivated in soil is between 6.0 and 6.8, with 5.8 to 6.2 considered the “sweet spot.” When growing marijuana in a hydroponics setup, it’s best to stay within the 5.5–6.5 range.

The pH of the water used on the growing medium of the plants affects their ability to absorb nutrients. For instance, most of the crucial nutrients, including nitrogen, phosphorus, and potassium (NPK), are only present when the pH of the aqueous solution is within the right range.

Within the aforementioned 5.8 to 6.2 range, for example, the availability of nutrients such as sulfur, calcium, iron, and magnesium is also at its highest.

If the pH of the growing medium gets too low, the solubility of nutrients like nitrogen decreases. In addition, the solubility of iron and manganese increases, which makes them more available to plants. However, since marijuana plants only need small amounts of these micronutrients, toxicity could occur.

Overall, if the pH levels are wrong, photosynthesis becomes less efficient. This has a negative impact on plant growth and performance. In a nutshell, you can anticipate more problems during the growing cycle, coupled with lower quantities of usable bud.

You need a pH meter to ensure that the soil and water in your marijuana garden are at the right pH levels.

Calibrating a pH Meter the Easy Way

There is no sense in having a pH meter if you don’t know how to calibrate it! Without regular calibration, your meter will provide inaccurate readings. Fortunately, the process is quite simple, as you’re about to discover.

Before proceeding, please ensure you have the following equipment (along with the pH meter and its instruction manual, of course).

  • Gloves
  • A transparent measuring cup (something like Pyrex is ideal)
  • Protective goggles
  • Distilled water
  • pH 4, 7, and 10 calibration liquid (this is because you need acidic, neutral, and basic points of standardization)

Calibration on the Acidic Side

Check the instruction manual and learn how to use the pH meter. Once you’re satisfied that you know what you’re doing, switch the meter on and enter “calibration mode.” Please note that getting to this stage will differ depending on the model, which is why you must read the instructions!

Wear your gloves and goggles, and pour a quarter cup of the pH 4 liquid into the measuring cup. Dip the meter into the solution and wait a short while. At this point, the meter should read 4.0. If it doesn’t, you’ll have to set the meter to 4.0 manually.

Finishing It Off

Things get extremely straightforward from this point onward. After the first calibration, clean the pH meter’s electrode with distilled water. Repeat the step with the pH 7 calibration liquid. When that’s successful, rinse the meter again and conclude with the pH 10 liquid.

Once you’ve completed calibration for all three pH levels, you’re good to go.

Using Your Freshly Calibrated pH Meter

The next step is measuring the pH of whatever you’re planning to add to your cannabis plants. Apart from the meter, gloves, and goggles, you also require the following:


  • A plastic syringe
  • pH up solution
  • pH down solution

Taking a Measurement

If you’re using a hydroponic setup, you can measure the pH of the bottled nutrients. When growing marijuana plants in soil, take a sample of soil from your plants. Mix it with an equal amount of the water you use for your plants to create a soil suspension.

Now, dip the pH meter into the nutrient solution or soil suspension. If the pH reading is in the optimal zone, you don’t need to do anything else.

However, if the reading is too high or too low, it’s time to act. For example, if the pH is 7.5, you’ll need to use pH Down, a concentrated acidic solution designed to lower the pH level.

Once again, the precise instructions will vary depending on the product. For instance, you may need to add 1 ml of the pH Up or Down product to a gallon of the nutrient solution or soil suspension.

Wait for the period outlined in the product’s instructions (usually between 15 and 30 minutes), and take a new reading. Keep adding the requisite product until the pH meter gives you the desired reading.

If you don’t have pH Up or pH Down, you can use alternatives to quickly adjust the chemical composition in the way you want. For example, white vinegar can decrease the pH (more acidic), whereas garden lime can increase the pH (more basic).

pH Meter Calibration: Don’t Feed Your Marijuana Plants Without Doing It First!

Monitoring the pH of your marijuana crop’s soil or nutrient solution is extremely important. Unless your goal is to kill your plants, it’s time to invest in a pH meter and learn how to use it. Proper calibration ensures that your plants have easy access to the nutrients they need to grow strongly. The result is optimal growth and a bigger yield.

Please note that you need to store your pH meter carefully. Its pH electrode is highly sensitive and easy to damage. Also, you must calibrate your meter regularly to ensure continued accuracy.

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