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Cannabis pH and Watering your Plants

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When growing cannabis, and almost any other type of plant, there are various factors that influence how they grow and the quality of the final product such as the quality of the air, water, sun and soil. Any sort of issue with the quality or presence of these parameters will generally produce poorly plants that are likely to catch more illnesses and/or be infested by insects or fungi. That’s why we’re going to be talking about pH for cannabis plants; pH is one of the most determining factors when it comes to feeding cannabis plants and having them absorb everything you give them.

What is pH?

pH is used to measure acidity and alkalinity of a liquid or dissolved solid. pH levels can range from anywhere between 0.0 and 14.0; substances with a pH lower than 7 are considered acidic, whereas those with a pH higher than 7 are considered more alkaline. If the solution is exactly 7.0, it’s pH neutral. A great example of an acidic substance is hydrochloric acid, which has a pH of 0.0, whereas caustic soda (washing soda) is highly alkaline, with a pH of 14.0. Water is the best example of neutral substances, as it tends to sit at around 7.0 pH.

The Importance of Measuring Cannabis pH Levels

When you put a lot of work and effort into growing cannabis in the hopes of obtained the best possible results. pH is an incredibly important factor when it comes to making sure that your plants are absorbing everything you give them via their roots. If your plants’ roots are not being given substances with the right pH, they won’t be able to absorb certain types of nutrients, and in a matter of time they may end up showing signs of deficiencies or excess, as certain types of minerals build up in the growing medium, creating a toxic environment for your plants’ roots while also stopping other nutrients from being absorbed.

If you manage to keep pH levels under check when watering, you still may end up with deficiencies or overwatering, although the probabilities of this happening are much lower and they’ll be much easier to fix if the pH is right.

What Should pH be for Cannabis Plants

For a cannabis plant to grow to the best of its abilities, you need to keep in mind that pH levels shouldn’t always be exactly the same; depending on the strain grown, the stage in which it is in (germination, growth, pre-flower, bloom), the growth medium and whether you’re growing organically or using minerals, the pH level of your water should vary slightly.

You can grow cannabis by keeping the pH at a constant level, although it’ll need to range between 5.5 and 7.0. This allows for decent results, although you won’t be making the most out of your seeds nor the nutrients you’re using to feed your plants. Plus, you may end up with feeding and nutritional issues further down the line.

These are the ideal pH values for growing cannabis in hydroponic and aeroponic settings including other inert substrates:

  • First weeks: 5.8 – 5.9 pH
  • Pre-bloom: 6.0 – 6.2 pH
  • Real bloom: 6.0 – 6.3 pH

These are the ideal pH values for growing cannabis peat mixes or straight in the ground:

  • First weeks: 5.5 – 6.0 pH
  • Pre-bloom: 6.0 – 6.2 pH
  • Real bloom: 6.2 – 6.5 pH

Adjusting pH for Cannabis Plants

Figuring out how to adjust the pH in your water isn’t that complicated at all. You need to discern between watering using nutrients and only water, and there will be a difference between using automatic watering systems and watering manually.

Using just water

Fill your tank or bottle, let the water sit for a few minutes and then measure the pH in the water using a pH meter. If needed, follow the instructions provided by the manufacturer of your pH Up or Down products. If there is no recommendation, add an extremely small amount to your water tank or bottle, dilute properly and let it sit before measuring it again. Repeat this process as many times as necessary until pH levels are as desired.

Water with nutrients

This process varies depending on the fertilizers used; some brands recommend adjusting the pH before adding their products, whereas others recommend measuring and adjusting the pH after adding them to your water. If the manufacturer has not left any specific instructions, we recommend dissolving your nutrients one by one, mixing thoroughly. Then, you’re going to need to let it sit for a few minutes in order for the pH to balance out. This way you can measure and adjust accordingly without any fluctuations.

Hydroponic watering

When it comes to automatic watering systems, a large tank is usually used alongside an automatic pipe system which usually contains water and nutrients, enough to feed your plants for about one to two weeks. In order to adjust the pH and keep it balanced within the recommended pH value, we recommend using pH and temperature monitors so that you can have an eye on the pH at all times. This allows you to easily and quickly adjust the pH when needed – all you have to do is keep an eye on it and you’ll be able to fix it before anything goes wrong.

Note: in order to avoid taking too long to adjust the pH in your water, we recommend writing down the original pH of your water and then writing down how much product was needed to get it to the right value. This will save plenty of time down the line.

How to adjust the pH in Water |The Best pH for Cannabis

Adjusting the pH in your water can be so simple that it gets complicated if you don’t have the proper tools and they aren’t in decent condition. In order to do this correctly, you’ll need to use a pH meter as well as specific liquid products used to adjust pH upwards or downwards. We’re going to have a quick look at pH meters and liquids used for adjusting pH.

  • pH Meters

pH meters are measuring instruments that are quite easy to use; most of the time, all you have to do is switch it on and place the sensor end in the water in order to analyze its pH. In order to avoid bad readings and issues with the meter itself, we recommend cleaning it after every use as well as adjusting them when necessary. Also, you’ll want to keep the sensor moist using a maintenance solution.

  • pH Adjusters

Liquids used to reduce or increase the pH in nutrient solutions contain either acidic or alkaline ingredients, which can be organic and/or mineral. Plus, depending on the manufacturer, some pH adjusters can be specific for the growth period or for the bloom phase.

Mineral pH adjusting products are generally made using the following ingredients:

  • Nitric acid: depending on the ratio, you can use this to increase or decrease pH levels, plus it’s perfect for the growth period thanks to its high Nitrogen count.
  • Phosphoric acid: this is used to lower the pH and it’s ideal for the flowering period thanks to its high phosphorus content, although it can also be used in the growth period.
  • Potassium hydroxide: this is used to increase the pH in water. Thanks to its high potassium content it can be used in the growth and flowering periods.

Organic pH adjusters tend to contain the following components:

  • Humic acids: these acids increase the pH in your water and can be used during the entire growing period, although we recommend using it during the growth period as humic acids can actually decrease THC yield.
  • Citric acid: this is used to decrease pH and it can be used during the entire growth and flowering process.

The main difference between organic and mineral pH adjusters is that the minerals tend to harm any natural life in the soil, so you need to rebuild it after every use. Organic products don’t have the same reaction, although you’ll need to use slightly more product than mineral products in order to get the desired levels.

Cannabis pH Meter Types

pH Testing Drops

This type of pH measuring kit is one of the easiest kits to use; all it contains is a vile, liquid reagent, and a color chart. In order to figure out the pH in your water, all you have to do is fill up ¾ of the vile using the water you want to analyze. Add in a couple of drops of the liquid reagent, and then place the lid on the vile straight away. Shake thoroughly for a few seconds and then text the color using the included color chart – this allows you to figure out the pH in your water.

We highly recommend keeping in mind that this type of reagent liquid can only be used in water without any nutrients or additives, as it will end up giving a false reading in such cases.

pH 600 ECO Milwaukee Meter

This is one of the most used pH meters on the market when it comes to indoor and outdoor growing rooms, as it’s the most affordable one and it provides good results. It’s a great way to get started when it comes to growing cannabis if you’re on a budget. You’ll need to calibrate it by using a calibration liquid – first, adjust it to 7.0 pH and then adjust it down to 4.0 pH. In order to adjust the pH to your calibration liquid, you need to turn the small screw that it has while checking the screen to make sure you’re adjusting it right.

The only downside to this meter is that you’re going to need to keep the sensor clean and humid/moist by using a pH meter maintenance liquid – if not, your meter will most likely start producing erroneous results when compared to other meters. You’ll also need to take into account that this device is not water-resistant, so do not let it fall into the water when using it.

ADWA pH AD-100 Meter

This pH meter is slightly more sophisticated than the previous model; as well as offering precise data, it can also adjust itself automatically when using pH 7.0 and 4-0 calibrators, which come included. It also has an automatic temperature compensation feature, which makes for much more precise measurements. This particular model is much stronger and more trustworthy as times goes on, although just like with any other meter, you’ll need to keep it humid and in good condition to avoid bad readings. The only inconvenience here is that it isn’t waterproof; all you need to do is place the tip of the sensor in the water.

ADWA pH AD-11 Meter

This AD-11 ADWA meter is a semi-professional model that, apart from precisely measuring the pH in your water thanks to automatic temperature compensation, also indicates the temperature of the water and can emerge unscathed if dropped in the water. This doesn’t mean that it’s entirely waterproof, and you still need to use the sensor part when measuring pH values. These water-resistant ADWA meters are quite prone to sensor issues, as they’re quite delicate, but you can easily get your hands on a replacement sensor. This allows you to keep one on hand just in case it breaks and your plants are at a delicate period.

In order to calibrate it, you’ll need to hold the ON/OFF button for a few seconds while it’s on until the letters CAL come up on the screen. Next, the meter itself will let you know what calibration liquid is needed – first, you have to use pH 7.00 and next you’ll need to use pH 4.00. In order to keep it in decent shape, you’ll need to clean it after every use and use maintenance solution when storing it to keep it working well and for much longer.

Guardian Bluelab Monitor

The Guardian Bluelab Monitor is, without a doubt, the most sophisticated, professional and precise pH meter found in this post; it’s a pH, EC and temperature meter that works continuously; it’s a great idea for hydroponic and aeroponic grow set-ups, as these types of grows tend to need a lot more control when it comes to the water used.

In order to use this continuous pH, EC and temperature meter correctly, all you have to do is place the monitor at head-height so that you can easily take a look at it, and then you’ll need to adjust the pH and EC in your water, depending on your plants’ needs and the period that they’re in. It also has a visual alarm system (a blinking light) that lets you know when the pH or EC in your nutrient tank aren’t at the right values, allowing you to correct almost any fluctuation instantly.

When you use any type of continuous pH monitor, you’ll end up saving loads of time when it comes to watering, allowing you to make the most of your cannabis plants’ potential. Keep in mind that the sensors can be replaced in case one of them breaks or is worn – you can easily replace them. In as far as its calibration system, it’s super easy – only the pH sensors needs to be calibrated in the exact same way as the rest of pH meters on the market. We recommend cleaning the sensors after every grow and storing them in maintenance liquid.

In order to learn more about the pH meters for growing cannabis plants in this post, you can go straight to their product page by clicking on their picture, allowing you to visualize the product better thanks to their concise, simple descriptions that make them incredibly easy to understand. Plus, we stock many more models that you can have a look at!

Measuring pH for Cannabis Plants has never been easier with these special devices made for easy and simple pH measuring. Models for all kinds of growers.

Wasser und pH

The pH is the measure of the acidity or alkalinity of a solution or substrate. A low pH shows that the solution is acidic and a high pH that it is base/alkaline. The middle value of approx. pH 6.8 is the neutral range. The pH is absolutely vital for all living organisms in various ways.

In the world of plants each plant species is perfectly adapted to a certain pH range of the soil or water. Hobby gardeners are usually familiar with the different pH requirements of various plants like rhododendron, roses, or conifers, and buy special soil mixes and regulate the pH of water appropriately.

Cannabis requires a pH range around the neutral value of 6.0-6.5 so that it can assimilate nutrients from the growing medium. In any cultivation the pH of the water must therefore be monitored and adjusted appropriately. A full point difference in pH represents a tenfold increase in either acidity or alkalinity. If you water on soil with pH 5.5 it is 10 times more acidic than pH 6.5! A pH below 6.0 can trigger a deficiency of calcium resulting in burnt root tips and black spots on leaves. A pH above 7.0 causes a deficiency in iron which results in chlorotic leaves and yellowing of veins. The assimilation of all major & secondary nutrients required by cannabis for healthy growth and flowering can be seriously affected by an incorrect pH. Most affected are phosphorous, potassium, magnesium, calcium, iron, and manganese. Read our Nutrient Problems Guide for more info on symptoms.

Photo: this is a standard colour chart for a liquid pH tester. The optimum pH range of water for cannabis cultivation in soil is a light green colour that indicates pH 6.2-6.5

Photo: electronic pH testers range from inexpensive, such as this model, to high-end. They are handy but can be less reliable than a liquid tester because you have to calibrate them regularly. For calibration you need to purchase calibration fluid for pH 4 and pH 7 and a simple thermostat.

Purchase your essential gardening kit.

SOIL: pH tester, EC meter, bottle of cheap vinegar (6° acidity), measurement cup for 10-100 ml
HYDROPONICS: pH tester, EC meter, bottle of cheap vinegar or pH UP & DOWN, measurement cup for 10-100 ml

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.

Take appropriate action if the water quality is low: a high EC or very low/high pH are indicators (i.e. pH below 6 or above 8). A household osmosis filter is the cheapest long-term solution to improving water quality if you have no other clean water source.


Measure the volume of vinegar * required for a fixed amount of water to adjust the pH down to 6.2-6.5. Add the required amount of vinegar each time you need to water and check the pH before watering.
If the water is too acidic (i.e. below pH 6.0) you should mix or replace it with another water source that has a higher pH. This could be bottled mineral water or rain water.
If you are using tap water let it sit in a bucket for a few hours so that the chlorine evaporates.

*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.


Add the required nutrients to your water until you have the appropriate EC (nutrient concentration) for your plants.
Measure the pH of the nutrient solution.
If the pH is still too high add vinegar
* or pH DOWN until the solution has the correct pH.
If the pH is too low add pH UP until the solution has the correct pH.
When you are using tap water let it sit in a container for a few hours so that the chlorine evaporates.

*Vinegar is a neutral acid that is completely harmless to plants when diluted in water. It can be used for Hydrofarms with hydro correls and on rockwool. Not all growing mediums may be suitable. run a test if you are using coco coir or other substrates.

Regularly check the pH and EC of your water if you are using tap water because there are sometimes larger fluctuations in water quality from municipal companies.

“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)

Many plant problems that are attributed by the grower to lack of fertilizer or poor genetics are in actual fact caused by the wrong pH of the growing medium or water (most often of water).

Failure to adjust the pH to the desirable range will result in several negative symptoms, that will range from mild to chronic, depending on the severity and duration of the pH unbalance:

  • single nutrient deficiency or multiple nutrient deficiencies causing any of the following: stunted growth, yellowing, dark blotches on leaves, small dark-blue leaves, contorted shoots, shriveled growth, leaf curl or burn, leaf drop, delayed flowering, low yield, etc.
  • higher ratio of males during sexing
  • appearance of male flowers on females
  • vulnerability to mold and fungus
  • vulnerability to pests

Fertilizing a plant that is suffering from a pH imbalance usually increases the cycle of problems. It may show a brief respite to symptoms, but only because the fertilizer added to the water may have changed the pH favourably for a short time. Without paying attention to the actual problem and adjusting the pH to the correct range your plants will continue to suffer and you will lose yield on a daily basis.

Due to the constant availability of nutrients in a solvent form in hydroponics there is a greater range of tolerance in pH fluctuation. Cannabis grows well hydroponically within a range of 5.5-6.5. Usually the pH is regulated to 5.8-6.0 for hydroponic systems with a growing medium that has been stabilized.

The ideal pH and pH fluctuation in hydroponics depends on several factors that you have to evaluate on an individual basis because each hydroponic system is different due to the following:

  • water quality
  • growing medium (coco coir, rockwool, hydro correls, mixture of several mediums, other substrates, or mainly pure water such as aero-flow and bubbler)
  • nutrient products used and their buffer capacity
  • additional products or buffer agents used
  • type of watering system & watering schedule
  • EC of nutrient solution
  • size of nutrient solution tank or plant container
  • room temperature
  • size of plants and their nutrient uptake

All of these factors influence how the pH should be adjusted and how it changes in the containers or tank over a period of time. A fluctuation of one full point in hydroponics can usually be tolerated by cannabis as long as the pH is stabilized to the ideal range within 24 hrs. For best results the pH should therefore be monitored daily in a system with large fluctuation.

Ideally your water quality should be good enough so that no or only minimal adjustment to the pH is required for a fresh nutrient solution.
Purchasing the correct fertilizer for your water quality helps in stabilizing the pH in your system. Several companies offer hydroponic fertilizer for either “hard” or “soft” water.

Photo: a standard pH kit for hydroponics includes a liquid pH tester, pH UP (potassium) and pH DOWN (nitric or phosphoric acid) for adjusting the pH range. Alternatively, vinegar can be used on some growing mediums to reduce pH if mineral salts are undesirable due to their effect on the EC of the nutrient solution.

Water quality

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.

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

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.

For a general assessment of your water quality test the pH and EC range with your essential kit. Also look at the colour of the water and if it has any strong smell. If you notice anything out of the ordinary you can give a 1L sample to the pharmacy for a chemical analysis. The pharmacy sells sterile bottles for this purpose. The analysis usually costs 50-60$/Euro and provides details of common harmful contaminants. This is especially recommended for testing well water. It helps to say that you need an analysis for drinking use and watering plants so that specific contaminants are tested for. If you need to install an osmosis filter for heavily polluted water you will need this analysis to purchase the correct osmosis system and filters.

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.

Photo: a typical household osmosis filter can be attached to any water faucet in your home or garden. The best buy is a 3-chamber system which contains three filters that can be replaced at relatively low cost.

Usually a household osmosis filter is sufficient to clean water from common impurities such as calcium, magnesium, and low levels of salts. The cost of 100,-$/Euro is worth the investment and cheaper than buying bottled mineral water. An osmosis filter system can last a lifetime and you only need to exchange the filters every once in a while. An osmosis filter is essential if your water has a high EC . Generally an EC above 0.7 is problematic, especially if you need to fertilize indoor or have a hydroponic system. Mixing your water approx. 50-50 with pure osmosis water solves this problem.

For germination and seedlings you should always use high quality water: “soft” mineral water with pH 6.5 and low levels of sodium is best. The pH should be adjusted to the ideal range with vinegar so that there are no salts which can inhibit germination or damage the seedlings. In hydroponics a very weak nutrient solution of EC 0.6 is usually used. For germination pure water is also sufficient until the seedling appears.

Lerne wann und wie zu düngen ist. Ein essenzieller Ratgeber der deine Pflanzen und Ernten schützt!

Wasser und pH The pH is the measure of the acidity or alkalinity of a solution or substrate. A low pH shows that the solution is acidic and a high pH that it is base/alkaline. The middle value