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ph for cannabis seeds

If you are growing hydroponically, test a sample from your water reservoir a few minutes after you add your nutrients. 🌊 Do I Need to Measure the pH of My Runoff After Feeding My Plants? Yes. Always remember to test the pH of your nutrient runoff as this will give you an idea of the pH of your medium. 🌈 How Exact Do I Need to Get My pH Levels When Growing Cannabis? Don’t get flustered if your nutrients are slightly below or above the optimal conditions we mentioned above. Only react to big changes in pH that may inhibit your plant’s ability to uptake nutrients.

pH measuring kits usually contain a test tube, a bottle of testing solution, and a colour-coded pH chart. Testing the pH of your soil with these kits is super simple:

By regularly checking the pH of your growing medium, you’ll be able to ensure that your plants are able to take up all the nutrients you’re giving them. You’ll also be able to catch any pH imbalances early, minimising your risk of running into nutrient deficiencies later on in your grow (more on that below).

Measuring pH With Drops

While using chemical nutrients might seem simple, it can actually take some time and practice to get the hang of properly fertilising your cannabis plants with liquid mineral fertilisers. Organic nutrients, on the other hand, naturally promote the health of your plants by supporting the development of healthy microbial life within your medium.

We’ve alluded to it already, but the best pH for growing cannabis resides within a narrow window. But, within that window, is there an optimal reading you should try to achieve? And, does that reading change depending on how you choose to grow? Let’s explore further.

pH imbalances are one of the most common causes of nutrient deficiencies in cannabis plants. As we mentioned earlier, cannabis plants can only take up certain nutrients within a small pH window. If the pH of your medium shifts below or above that ideal window, your plants won’t be able to take up the nutrients in their fertilisers and will start to show signs of a nutrient deficiency.


pH Down is an acid based formula for lowering pH. General Hydroponics up/down is made from a base of Phosphoric Acid.

pH Up is a strong alkali formula for raising pH. The one from General Hydroponics is made from a base of Potassium Hydroxide and Potassium Carbonate.

As explained above, adjust the pH of your solution a little at a time. Try to use only either Up or Down. If you overshoot with one and then have to readjust with the other you can end up unnecessarily stressing your plants. Mix up a little of the required pH adjuster in a separate jug. Then add them a little at a time to your reservoir. Allow time for the whole reservoir to even out and settle. Better to get it right with 3 slight adjustments than have it wildly swinging up and down.

Photo: yellowing, leaf curl, circular burnt spots on leaves, and leaf drop are typical symptoms from water with a high level of sodium.

*Vinegar is a neutral acid that is completely harmless to plants when diluted in water. It should be used to adjust the pH of the water for soil cultivation to prevent overfertilizing of plants. The commercial pH DOWN products all contain potent nitric or phosphoric acid that raise the salt level in soil and can burn your plants. Especially seedlings and young plants easily suffer from regular watering with pH Down.

Your municipal water board can provide a free chemical analysis of the tap water in your neighbourhood if you request it because they regularly perform these tests as a standard procedure. Usually this is not necessary for you to look into unless the water is very poor quality or running through old pipes that pose a health hazard.

Tap water can be “hard” from high levels of calcium (Ca) and magnesium (Mg). The pH is in this case very alkaline. Chlorine is another common additive which causes stunted growth in plants and acidifies the soil. If your tap water smells from chlorine you should fill warm water into a bucket and let it sit for a few hours so that the chlorine can evaporate.

Test the quality of your water by checking the pH and EC range. Take into account any unusual colour or smell of the water. Make a chemical analysis at a pharmacy if you think your well water or tap water is heavily contaminated.

“Incorrect pH belongs to the most serious nutrient disorders in organic-soil gardens. Many complex biological processes occur between organic fertilizers and the soil during nutrient uptake. The pH is critical to the livelihood of these activities.” (Marijuana Horticulture, Jorge Cervantes)

Tap water and well water are two main sources that need to be checked for quality. Both can be contaminated with toxic levels of minerals. High levels of sodium (Na) are often found in well water and can cause excessive damage to plants. Saline water on the whole must be avoided.