If the grower aims to grow his plants on a truly professional level and thus monitor the proper course of their growth and flowering, he should definitely know what quantities and values to control - one of them is the pH value.


In general, pH determines whether water or soil is acidic, neutral or alkaline. We determine the pH values on a scale from 0 to 14, with values 0–6.9 meaning acidic water, a value directly equal to 7 being neutral and values 7.1–14 being basic values. 

Just to give you an idea: acidic pH values are found in lemon juice or vinegar, for example - on the contrary, slaked lime has high pH values and the ideal pH for the human body is neutral - ie 7. 

However, the whole scale is not suitable for cannabis cultivation - neither as soil pH nor watering watering. As for the pH of the soil, it should be in the range of pH 6-7. The correct pH value of the irrigation then stabilizes the pH of the soil more and we will get closer to the desired value.

Today we will deal with the control of the pH value of the soil, because it is needed especially for outdoor growers, who are slowly but surely starting the season, and also for guerrilla growers who plant plants in less accessible places and public areas and who are currently they are already starting to look for their boxes. 

And why is it essential to control pH values? Because with the right values, plants can absorb and consume specific nutrients as much as possible. This makes some macro or micro elements easier for plants to reach - but more on that next time.

Again, I would like to avoid comparing all sorts of substrates in hobby markets and horticulture, but a few tips will certainly come in handy. 

If you have already decided or are forced to buy substrates in a hobby market, always look at the back of the package, where this value is stated. Thus, for example, substrates for cacti and succulents which have a very low pH are completely unsuitable. Therefore, the first thing that will interest you when buying a substrate in ordinary gardening is always this value.

Another thing to watch out for, especially when growing outdoors, is where you will plant the plants. In forests and forest nurseries of conifers or around peat bogs, the pH of the soil is very low. The only solution is to transport, for example, dolomitic limestone, bone meal, horn or wood ash into the soil.

Conversely, if the pH of the soil is too high - alkaline, you can reduce it by adding needles, peat, composted leaves from trees or grated lemon peel. 

When it comes to measuring soil, you can proceed in three ways, the first two being cheaper but more time-consuming, and for the third we will have to dig a little deeper into our pockets.

Soil pH measurement using paper strips

You can get these strips in every aquarium and in the vast majority of grow shops and it is the cheapest pH test that can be purchased, usually up to CZK 100, but also more depending on the number of strips. They are mainly used to measure the pH of water, but if you know how to do it, they can also be used to measure the pH of the soil - and it's not difficult. 

To measure pH using these strips you will need distilled water, pH test strips, a spoon and a handful of soil from the flower bed or pot you want to plant. 

Take a pint glass or measuring cup and fill half of it with the soil you want to measure. Fill in fully distilled water and mix thoroughly with a spoon. Leave the soil on the bottom of the glass for a few minutes and place the test paper in the liquid section for about 30 seconds (depending on the manufacturer of the particular paper). After removing the paper from the water, it turns a certain color. Compare this color with the enclosed color legend that was included in the pH tester package and compare. The closest color match of the paper with the attached legend corresponds to the pH of your soil. However, the disadvantage of these testers during closer measurements is that they are only in the range of pH 0.5, for more accurate measurements you can use liquid pH testers. 

Soil measurement using liquid pH testers

These liquid pH testers can be purchased mainly in grow shops and their price ranges from 150 to 200 CZK, but this test is not enough for more than 5-7 accurate measurements. These testers contain a test tube, an indicator solution and a color legend instead of strips. Again, they are mainly used for measuring water, but if you want to measure pH more accurately than with paper strips, they will be a bit more expensive for you, but a better choice, as some of them measure with a pH deviation of only 0.2.

As we progress, we will have to improvise a little more. The manufacturers of these testers usually supply a test tube with a size of 10 ml in their set - but this is not enough for a correct and accurate measurement. It is usually recommended to fill this tube with water and add 3 drops of indicator solution, shake and compare the color of the measured water with the color legend in the package with the tester - but this only applies to measuring the water itself. 

In the case of soil measurement, it is different - a test soil sample simply cannot fit into a 10 ml test tube. The vast majority of liquid pH tests come with a 30 ml bottle of indicator solution, which corresponds to about 150-180 drops.

In this case, it is ideal to fill half a 200 ml glass with the soil you want to measure. Then we measure the amount of distilled water, which we add to the glass so that it is full - an estimated 120 ml, for example. 

Then mix the glass with the soil sample thoroughly and let it stand for a few minutes. Take a T-shirt, coffee filter or cloth handkerchief, filter the soil from the water and squeeze the soil in a handkerchief or T-shirt and mix the solution again.

Since we added 120 ml of distilled water to the glass and the dilution is three drops of indicator solution per 10 ml of control liquid, we reach 40 drops of indicator solution, which we add to the glass and mix thoroughly again. After a while, the water in the glass starts to color and we compare the resulting color again with the color legend, which was part of the pH tester.

Measurement using electrical pH meters

In this case, we distinguish between pH meters, which are for measuring water, and pH meters, for measuring soil, which are the most accurate. 

When using pH meters to measure water, we proceed very similarly to that of liquid pH testers. Put a control sample of the soil in a glass, add distilled water, let it sit, filter and measure the liquid. The resulting value will be with a maximum deviation of 0.1, for more accurate pH meters for water measurement 0.01.

For pH meters for soil measurement, the values are the most accurate, as no medium is used here - in our case distilled water, which could change the values. In any case, when measuring soil with pH testers and pH meters for water measurement, always try to keep a 1: 1 ratio of distilled water and measured soil to make the values as accurate as possible.

Keep in mind that the values measured with pH meters for water measurement are always indicative only, and you can only measure the exact pH of the soil using a pH meter designed directly for the soil. 

The measurement with these pH meters is also the fastest and takes place by inserting the probe of the pH meter into the soil and the exact value will appear on the display after a while. However, these pH meters are relatively expensive and not so often used, but if you want to have a clear conscience or become a true professional in the field, I highly recommend them. 

On the other hand, if you don't want to worry about the pH of the soil in your garden, field or growing box, I recommend buying a quality substrate from a growshop, which always has values precisely adjusted for growing cannabis.

Either way, I wish everyone the pH of the soil at the best levels, guerrilla growers the right choice of place and everyone else well-being and a smile on their face ☺


"If you decide or are forced to buy substrates at a hobby market, always look at the back of the package for the pH value"

"Keep in mind that the values measured with pH meters for water measurement are always indicative only"