Have you ever wondered why pH and EC are so crucial to the success of your crop? In this article we will talk about what pH and EC are. If you read on, we’ll guide you through how these factors directly affect your grow and how to measure them. Get the perfect growing conditions for your plants… and take your crop to the next level!

Measuring the pH of a nutrient solution.
Measuring the pH of a nutrient solution.

What is pH? A Simple Definition

You’ve probably seen references to “pH” on many occasions: in growing, in your shower gel and even when talking about swimming pools. But do you really know what “pH” means?

 

“pH” stands for potential of hydrogen and is a coefficient representing the concentration of hydrogen ions [H+] present in a solution. Depending on the number of these ions, the pH will be lower or higher. And yes, this number is more important than you think, as it indicates how acidic or basic a solution is.

 

The pH Scale: 0 to 14
The pH is measured on a scale ranging from 0 to 14:

● If the pH value is below 7 it is acidic.
● If the pH value is above 7 it is alkaline or basic.
● A pH value of 7 is neutral, like that of pure water.

The difference between acidic and alkaline substances is real and palpable in our daily lives. From lemons to wines, many of the foods we eat have a slightly acidic pH – even our stomach has hydrochloric acid with a pH of 3,5 to aid digestion! On the other hand, highly alkaline substances, such as ammonia or bleach, are more from cleaning equipment than from the pantry.

The pH scale is logarithmic and ranges from 0 to 14 as a function of the amount of [H+] present in a solution. 
The pH scale is logarithmic and ranges from 0 to 14 as a function of the amount of [H+] present in a solution. 

What is the importance of pH for plants?

Plants live best in a slightly acidic root environment. This has to do with the availability of nutrients in the soil according to pH.

 

The pH of the substrate directly affects the availability of nutrients in the rhizosphere and their uptake by plants:

Macronutrients such as nitrogen, potassium, calcium, magnesium and sulphur show higher availability at pH 6.0 – 7.0.
Micronutrients are more available at more acidic pH values (pH < 6,5).

Macronutrient and micronutrient availability is maximised at pH < 7.0
Macronutrient and micronutrient availability is maximised at pH < 7.0

Therefore, the pH value for optimal nutrient uptake should be slightly acidic, ideally around 6.0. While it is true that there are plants that need somewhat more acidic substrates (acidophilic plants), there are others that tolerate more basic soils, but not that they develop better in them.


Fun fact: There are plants such as hydrangeas that vary in color depending on the pH of their flowers. In a slightly acid substrate (pH 5.5 – 6.5) the flowers will be purple, mauve or magenta red. At a more neutral or slightly alkaline pH (pH 6.5 – 7.5) pink or white hydrangeas are more likely.

 

Measuring pH: How should I measure the pH?

Controlling pH is key because of the above. How do you do it? Well, there are tools and meters that will tell you the pH value of your solution.


It’s important to know the pH of the nutrient solution you are watering your plants with and always keep it between 5.5 and 7.0. Equally important is to know the pH of your substrate. Ideally, if your substrate doesn’t indicate the pH value on the label, or if you are using your own substrate, you should measure it yourself.


We use the Dutch method, which consists of a 1:1.5 extraction. This means that for every 100 ml of sample, we use 150 ml of distilled water to dissolve it. This is the method we use to measure the pH value of our substrates, and you can always find it on the label of our bags. Here are the steps to follow!

Tool used for the extraction of 100 ml of substrate following the Dutch method: 3 cylinders; two hollow cylinders that act as containers, the small cylinder being the one that holds exactly 100 ml, and s non-hollow cylinder that we use as a weight.
Tool used for the extraction of 100 ml of substrate following the Dutch method: 3 cylinders; two hollow cylinders that act as containers, the small cylinder being the one that holds exactly 100 ml, and s non-hollow cylinder that we use as a weight.

1. Take substrate samples. If you want to measure the pH of a bag of substrate without the pH value, simply take a sample from wherever you want. In the case of reusing substrate, wash and treat it before testing, so you can determine whether the pH value of your substrate is optimal for reuse. If you want to calculate the pH of your garden soil, you should take samples from the different parts of the soil that will be found around the roots. Not all areas of your garden soil will have the same pH. Therefore, it is ideal to take soil samples at shallower and deeper depths. Take the samples and mix them all together evenly.


2. Dose the solid sample. Here comes the key, because the substrate is solid, so it’s quantified in grams, but we need to measure it in ml. To do this we use a special tool that allows us to extract 100 ml of substrate.


How? By using the cylinders, we compact the substrate sample to collect only 100 ml of it. When it’s pressed into the 100 ml cylinder, we separate it using a spatula, as shown in the sequence of images below.


3. Add distilled water. Put the mixture in a container and add distilled water. The dilution ratio varies from method to method, but we use the Dutch method so we will mix 100 ml of substrate with 150 ml of distilled water (1:1.5).


4. Stir well and let it stand for 10-15 minutes.


5. You can then strain the mixture and take the measurement with the resulting liquid.

Dutch method process showing the collection of 100 ml of substrate to be used for further measurements.
Dutch method process showing the collection of 100 ml of substrate to be used for further measurements.

The tool to measure the pH is up to you.

● Using a pH meter. These electronic devices are reliable, but require care and maintenance. Cleaning and calibration of the meter is essential from time to time as the reliability of the results depends to a large extent on being diligent with the maintenance of the meter. The materials and instructions for maintenance are usually included in the kit itself. Generally, these are durable and accurate devices that are well worth the cost and maintenance.


● Using pH paper strips. This is a less accurate, but also useful method. These paper strips are impregnated with specific chemical indicators which, when they come into contact with the solution, react with its pH by changing colour. Once the process is complete, we must compare the final colour of the paper strip with the included colour scale to determine, approximately, the pH value of the solution.

Comparing the pH strip with the scale included.
Comparing the pH strip with the scale included.

The EC, What Is It and Why Is It Important?

EC (Electrical Conductivity) is another key player.


EC is a measure of the salinity of a liquid sample. The nutrients you add to the water are mostly salts, and the more nutrients (salts) in the solution, the higher the EC reading. Therefore, by measuring the EC of the irrigation water you can get an idea of the amount of nutrients dissolved in it and whether the value matches the needs of the crop.


Avoiding over-fertilisation is key so that the plant does not suffer from excess or toxicity of any element, and it is equally important to know that you are giving them enough nutrients. This is why it’s important to control the EC of your nutrient solution.


However, to do this correctly you must have some guidance on what EC values are appropriate for the needs of your plants and how to measure them… so let’s go over some general criteria!

 

How to Measure the EC?

To measure the EC it’s necessary to get an EC meter. These will also need to be maintained, and the materials and instructions for doing so are usually included in the kit.There are devices that can measure both pH and EC, so you don’t need two separate meters.

There are many types of measuring devices that can measure pH, EC and even temperature.
There are many types of measuring devices that can measure pH, EC and even temperature.

The first thing to know is that the most common unit for measuring EC is the Siemens per centimetre (S/cm). As EC values are usually very low, it is common to find Siemens expressed as milliSiemens (10-3) (mS/cm) or even as microSiemens (10-6) (µS/cm).

 

Then, it’s as simple as inserting the EC meter into the nutrient solution while preparing it. Then, as you add nutrients, you can monitor the increase in EC until the desired value is reached. If you wish to reduce the EC, do it by adding to the solution more distilled water.

 

If you want to check the EC of the substrate, simply repeat the process explained in the pH section, but this time instead of measuring the pH, measure the EC. This way you can see what the real EC value of your substrate is.

 

But why do many sites recommend me to measure the drain water?
For us, checking the drain water isn’t so reliable. We can use it as a complementary method of control, but not as the only method.

 

This is because, in addition to the fact that the plant will absorb nutrients, these also interact with the medium – especially in peat substrates – and, therefore, the values you obtain will be distorted. This is why we consider it to be ineffective in controlling the amount of nutrients your plant receives.

 

How to Adjust the EC for Your Plants?

Once the above is clear, it’s time to put it into practice.

 

Adjusting the electrical conductivity of your nutrient water is not a difficult task if you are clear on the basics. If you’ve made it this far, you’ve already soaked up the theory, and you’ll master the practice in no time!

 

To adjust the EC, the first step is to know the EC of the water you use for irrigation.

 

If this value is too high, you can use a reverse osmosis system (RO syste), or add distilled water to the tap water to reduce its EC.

 

When you start with pure water, you should increase the EC to 0.4 mS/cm ONLY with calcium and magnesium supplements like Calmag. These essential elements are present in tap water, but not in purified water.

 

Then add all basic nutrients and stimulators to achieve the desired final EC.

 

The EC depends on the type and method of cultivation, along with the stage of the plant’s cycle. The guideline below is a very general one for a pot culture:

During germination: it can start from 0.8 mS/cm rising slowly until the plant is ready to be transplanted.
● During the vegetative growth stage, you can adjust an EC of 1.2 mS/cm up to 1.5 – mS/cm when the plant starts to flower.
● During flowering its nutritional needs increase, so the EC should be raised to 2 mS/cm, and can reach up to 2.5 mS/cm in the last weeks of flowering.

 

For hydroponics, slightly higher EC values are usually sought.


Consider that the amount of nutrients a plant requires doesn’t only depend on the phase of the cycle it’s in. Its size, leaf volume and pot size also play a role, hence the range of values. The larger the plant, and the bigger the pot it is in, the more nutrients it needs and the slightly higher the EC.


And that ‘s it!
Now that you have soaked up all the theory related to pH and EC, do you feel better equipped to face the challenges of growing your crop? Remember, balance is key, and measuring pH and EC are your secret weapons. Happy growing! 🌱

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