pH and cannabis

When you start growing cannabis, one of the first things you learn is the importance of the pH of both the substrate you are going to use and the irrigation water, especially if you are growing in coconut fiber or other hydroponic media. And, to achieve the best results, every detail counts, and the pH of the growing medium (and, of course, the irrigation water or nutrient solution) is one of the most critical factors for the success of the crop. From root development to nutrient absorption, pH balance plays a critical role in every stage of your plant's life cycle.

In this article, we'll explore in depth the importance of maintaining proper pH in your growing medium, from how it affects plant growth and health to how you can effectively measure and adjust it. Get ready to delve into the world of pH and discover how you can optimize your crops, maximizing the yields of your plants while avoiding possible problems of nutrient deficiencies or blockages.

 The pH level of a substance determines its degree of acidity or alkalinity
The pH level of a substance determines its degree of acidity or alkalinity

What is pH?

pH is the negative log used to know and determine the acidity/alkalinity of aqueous solutions by calculating the H+ (Hydrogen positive ion) activity in the solution.  This scale has been developed from standard solutions with stabilised and known pH by international agreement.

Definition and measurement of pH:

pH = - Log 10 (ªH+) = Log 10 (1/ªH+)

The pH range or scale is divided into 14 values; pH 7 is considered to be neutral, a pH value of less than 7 is called acidic, and pH values greater than 7 are considered basic or alkaline.

Influence of pH values on cannabis crops

As also happens in humans, plants have pH fluctuations in their metabolism, which mainly depend on the pH range and stability. Thus, cannabis plants have a better or worse development and overall health state depending on the pH, being more or less sensitive to pests and diseases.

Regarding marijuana plants, we could speak about pH as a stopcock that regulates nutrient uptake and determines which nutrients are available for the plant.

The pH value used when growing marijuana mainly depends on the type of substrate used; if we grow in soil and using organic nutrients we can be less precise than when growing with mineral nutrients or inert substrates. Some growing mediums are not suitable for growing cannabis due to their pH value or nutrient composition.

pH in organic cannabis crops

Naturally, the soil has the capacity to control and maintain the pH level, which is called the buffer effect. This capacity helps to keep the rootball healthy and protected thanks to a pH range suitable for the growth of cannabis plants. We can check our substrate pH by performing tests, although it is usually indicated on the bag.

This buffer effect is caused by the microbial life in the substrate, which helps to balance pH fluctuations while maintaining it within optimal values during the whole crop and without the need to use acidic solutions to lower the pH, which often destroys this beneficial life.

An adequate pH adjustment in the substrate and irrigation water will lead to abundant harvests and plants without nutritional problems.
An adequate pH adjustment in the substrate and irrigation water will lead to abundant harvests and plants without nutritional problems (Image: Spencer Gray)

If we are using an inert substrate like coco, the pH value will be much more unstable. To maintain optimal pH values we can use pH up / down solutions in our nutrient solution, so we can adjust the pH - with the help of a pH meter - to the desired value.

This also happens when using water with pH values too low or too high for the proper development of our plants.  To adjust the pH, use organic solutions such as citric acid to lower it and silicon-based solutions to raise it.

As happens with the nutrients, every bacteria has its optimal pH value to develop correctly, so using a pH range from 6.5 to 7.5 when growing in soil is recommended for best results.

On the other hand, if we're using mineral nutrients we must be more careful with the pH value of the nutrient solution, otherwise, our plants will not have available all the needed nutrients. Since most mineral nutrients are chelated, there's no need for the microbial life of the substrate to process them before the plant assimilates them.

If we use soil and mineral nutrients, the pH value should range between 6 and 7, depending on the stage and needs of each plant.


pH in hydroponic cannabis crops

In hydroponic crops, the pH value is as important as the amount of nutrients given to the plant. The pH value must be adjusted for each stage of the plant so it can properly absorb nutrients in every irrigation.

During the growth stage of seedlings and young cuttings, a pH of 5.5 is recommended. We can raise this value up to 5.8 as the plants grow. During the stretch (pre-flowering stage) the plants start to demand more and different nutrients; we can raise to 5.9 now. In this way, plants have all the necessary nutrients to grow and start flowering without a problem.

Tips to avoid stretching cannabis plants

To control the height of the plants is a crucial aspect in cannabis cultivation, especially indoors, but also outdoors if discretion is needed. In this article we tell you some tips to avoid (or promote if necessary) stretching plants, particularly at the beginning of the flowering stage.

During the bloom period, we should use a pH range from 6 to 6.2 for more efficient nutrient uptake. During the last weeks of this stage, we can raise the pH value to 6.3-6.4.

When pH values are not correct, all plants in general have fewer nutrients available, so they lose their store of nutrients and begin to show deficiencies (which may also come from nutrient lockouts). We must always think that if plants don't have the correct pH value they'll show nutritional issues sooner or later.

Soil pH

Some substrates don't have a correct pH value for marijuana plants, a problem often caused by the composition of the substrate. We have two options here

  • First of all, perhaps the simplest solution is to purchase a quality substrate designed for cannabis plants. These types of substrates have a perfect texture for root development and a pH value of 6.5, ideal for growing marijuana.

tabla-rango-PH-tierra-e-hydro (1)
pH range in soil and hydro

  • The second option is preparing a good substrate by mixing several types of substrates; we need it to be spongy, rich in nutrients, and easy to drain and manipulate. If we don't have a good substrate it doesn't matter how good our seeds or nutrients are, our results will always be poor.

The most common amends are worm castings, coco, peat, perlite, and compost. The type of amendment used mainly depends on the composition of the base substrate.

What pH should I use with foliar fertilizers?

Foliar fertilizers are increasingly used for their easiness of use and fast absorption by plants.

As happens with the roots, we have to adjust the pH of the nutrient solution in order to achieve the best possible nutrient uptake by the leaves.

In this case, the pH value should range from 5.5 to 6.5, so plants will assimilate the NPK content much better. If we don't adjust the pH value, fertilizing our plants is almost useless since they can't absorb nutrients correctly.

Foliar feeding should always be combined with irrigations, otherwise, the plant may get used to being fed via foliar and its root system won't grow as it should.

On the market you will find all types of meters, even with automatic adjustment according to the pH value you enter.
On the market you will find all types of meters, even with automatic adjustment according to the pH value you enter

pH meters

We always recommend using electronic pH meters to measure the pH value of our nutrient solution. You can find either manual or continuous meters, which have a probe in the reservoir and continuously offer the current pH value of the nutrient solution on a display.

These continuous pH meters enable the user to replace the probe in case of failure or damage so we can have precise readings again. These meters have to be periodically calibrated with standard liquids with known pH values.

If we don't use a reservoir but want to check the pH value of our nutrient solution we can use manual or portable pH meters, which are battery-powered, small, and precise. In this way, we can carry our pH meter wherever we need and adjust this crucial parameter anywhere.

Happy harvest!

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “pH and cannabis” (6)


Jennys herbd 2022-08-31
What is the name I need to buy PhD minus or plus. I can't find the solution to add toy water to raise or lower my PhD

Alchimia Staff

Tim Alchimia 2022-08-31
Hi, thanks for your question. You'll find the items you need in our pH control category, where we have products to raise the pH of your irrigation water/nutrient solution, such as Terra Aquatica pH+ or to lower the pH, like BAC pH Down. I hope that helps. Best wishes and happy growing!


Elli 2022-07-18
What ph level is optimal during bloom phase in soil? I was thinking 6.5 or 6.6

Alchimia Staff

Tim Alchimia 2022-07-18
Hi Elli, thanks for your comment and question. In soil, anything from 6-7 is fine but try and aim for between 6.2 and 6.5 during the full bloom phase of your plants. I hope that helps, best wishes and happy growing!


Chuck 2021-08-27
My veg. PH is 5.6 should i raise it? My bud rm is at 6.2 to 6.5 4 weeks in bud is this going to be ok?

Alchimia Staff

Tim Alchimia 2021-08-30
Hi Chuck, thanks for your comment. Are you growing in hydro, coco or soil? With coco, normally, pH is adjusted to 5.5 - 5.8 during growth and 6.0 - 6.3 during bloom, which helps the plant to assimilate the most demanded nutrients at each stage. In hydroponics, the margin is a little narrower, between 6 and 6.4. In soil, there's more margin, with levels ranging from 6 to 7 pH. I hope that helps. Best wishes and happy growing!


-Aman L. Is an Alchimia client 2020-04-24
Bonjour, J utilise Advance Nutrients comme engrais en hydro, la gamme pH perfect. Mon soucis en résumé: après avoir eu un pH stable à 5.3 pendant 48h, il a subitement augmenté de 1.7 en moins de 12h alors que j avais rien touché. 5.3 Pendant 48h (on est passé de 6.8 avec engrais à 5.3 donc -1.5 grace au pH down). Pendant 2 jours ça reste à 5.3 . 12 heures après ça monte à 7.0 Le pH down liquid utilisé conseillé par tranche de 0.5ml/l - malgré le res. 140 L j ai mis la moitié donc 35ml. Ça a bien baissé de 6.8 -> 5.3 et resté stable 48h La température de eau est OK entre 20-23 degrés. Aussi, j attend minimum 1h avant chaque mesure. L EC ne bouge pas, juste une grosse fluctuation/baisse de pH. Je veux éviter de rajouter du pH moins à tout prix même si il est organique. Dois-je vider le bac? Pour quelle raison est il remonte aussi rapidement après avoir été stable, un conseil pr aider à stabiliser? Merci par avance salutations,


OKAI WISE KWESI 2019-06-11
Hello, i really want to farm cannabis and have already started. But my problem is how to get materials for the work. I am a Ghanaian. I will be very happy if we can establish a good relationship so that we can help each other.Please kindly reply this message whether you are interested in doing business with me or not.Thank you


Papa Indica 2015-07-02
As I've mentioned in another post, I have a cousin who lives nearby who is also an indoor grower, over the years we've worked together a lot to refine our grows. We both grow in soil and spend the money for good stuff, using organic mediums, (and always using lime). I've never had ph problems, and my cousin hadn't either but, for some reason, he decided to try and start controlling the ph levels in his grow. All he ended up doing was to make a big mess of things. So, if I could give one piece of advice it would be this; if you don't have a ph issue, don't try to create one. Happy growing! :^]_~

Alchimia Staff

Dani Alchimia 2015-07-02
Hi Papa Indica, We always say "if something works, then don't touch it"...Once you decide to check your pH, you need to always have a correctly calibrated meter, otherwise, as you say, you'll create a problemm where you never had one. pH should always be checked if nutritional problems show up, so we can know what is exactly assimilating our plants. Thanks for participating in our blog, All our best vibes!

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