Hydroponic Growing Technical Guide

Those of you who follow us at Gardenprue will surely remember an entry we made about hydroponic cultivation . It was more focused on home growing and starting in a basic way. Today we are going to comment on some things in a more technical way to gradually introduce ourselves into the world of hydroponic cultivation  in which we will gradually add more information. Are you up for it?


  1. There is a greater control of nutrition in the plant since there are no interactions by the soil (structure, pH, biology, salts, etc.).
  2. As it is a closed system where the contributions of water and minerals are recycled, the use of resources is very high.
  3. There are many more alternatives for substrates and mineral contributions than with respect to traditional soil cultivation.
  4. Absence of some common diseases caused by contact with agricultural soil (fungi that live in the soil).
  5. Similar uniformity in the crops by having the same water and the same nutrient solution, and not being influenced by any external characteristics generated by the soil.
  6. Productivity increase.
  7. Increased crop development and earliness.
  8. Increases the ease of harvesting the crop.

Eeeeehhh! Are they all advantages? Of course not, there are also some drawbacks:


  1. You generate plastics and waste in a much greater quantity than in soilless cultivation.
  2. The substrates, being innocuous, generate greater problems with respect to root diseases. That is, they appear less likely (as we have said before) but when they do they cause more problems.
  3. Need to carry out an exhaustive and permanent control of the installation. In agricultural soil, failures are better tolerated, but in hydroponic cultivation, a failure can mean the total loss of the crop.
  4. Higher installation cost. Substrates, irrigation, structure, containers, etc.
  5. Great technical advice due to point 3.

A curious way to hydroponically grow tomatoes
Source: Kathy Kimpel

What substrate to choose?

In the market there is a great world of substrates, each with its own particular properties, including (although it may seem curious to you) water. In this article we made a large part of the substrates that you can buy appear .

If you are still interested in knowing all the substrates that can be used, the Ministry of Agriculture offers you the possibility of knowing the main characteristics of each one. You can do it here . There are so many!

Choosing one or the other depends on the crop. All the characteristics of each must be taken into account, but generally what is required of a substrate for a soilless crop is a  high retention capacity, rapid drainage, good aeration, low apparent density, stability and particle size distribution. .

Aeration capacity

This means that the substrate must contain air after watering, so that root suffocation does not occur The ideal value with respect to the aeration capacity is between  20 and 30%. 

Available water

The available water is the water that the plant can use without difficulty once it has been properly watered and drained. This value is influenced by the water tension and significantly affects productivity. An optimal value can be between 20-30%.


With porosity we refer to the free space that must exist in a substrate for it to be occupied either by air or by water (with nutrients). To be optimal, it must have a porosity percentage of 85%.

Particle size

The size of the particles is a very important factor that, in fact, we have discussed within the main characteristics that a good substrate should have. This factor determines the porosity or free space in the substrate, and the larger the particle size, the greater the space. We want a porosity of 85%, so the size of the particles must be between 30 and 300 microns.


A substrate can positively or negatively influence the pH value and affect the crop. The organic substrates , such as land, have higher buffering capacity, that is, greater resistance to change its pH. For a crop to develop correctly we will have to know the correct pH for growth, and we can know that from this article on the Ph of plants  . It will normally be between 5.5 and 6.8.

In order not to make this too heavy, instead of putting the properties of each substrate here, we will dedicate an article to each one and add it to this entry, so that it can be consulted comfortably.


Although there are surely many more, these are the most used:

  • Magnesium nitrate: MgNo3 6H20
  • Calcium nitrate: Ca (No3) 2
  • Potassium nitrate: KNO3
  • Monoammonium phosphate: NH4H2PO4
  • Phosphoric acid (100%): H3PO4
  • Nitric acid (37%): HNO3
  • Magnesium sulfate: MgSO4 7H2O
  • Potassium sulfate: K2SO4
  • Monopotassium phosphate: KH2PO4
  • Phosphoric acid (37%): H3PO4
  • Ammonium nitrate: NH4NO3
  • Nitric acid 100%: HNO3

 4 examples of nutrient solutions in 1,000 L 

Nutrient solution 1:

  • Lime nitrate: 49.4 kg
  • Potassium nitrate: 38.4 kg
  • Microelements: 2 kg

Nutrient solution 2:

  • Potassium nitrate: 31.8 kg
  • Ammonium nitrate: 4 kg
  • Phosphoric acid 75%: 12.3 L (liquid)

Nutrient solution 3:

  • Potassium nitrate: 36.6 kg
  • Potassium sulfate: 16.5 kg
  • Microelements: 2 kg

Nutrient solution 4:

  • Potassium nitrate: 32.1 kg
  • Potassium sulfate: 1.4 kg
  • Monopotassium phosphate: 20.4 kg
  • Magnesium sulfate: 35.9 kg



There are a series of measurements and periodic checks to see if everything is correct and we have not made a mistake in choosing the substrate, the amount of irrigation or the type of subscriber. Let’s see it case by case:


The drainage of the substrate in hydroponic cultivation is determined by the amount of irrigation water and the characteristics of the substrate. One way to calculate drainage and see if everything is okay is to do the following:

  1. See the amount of water with which irrigation starts. Example: 100 Liters
  2. See the number of drippers, sprinklers or irrigation means we have. Example 4
  3. See the amount of water that returns to the source, that is, that is recycled: Example 85 liters.
  4. Calculate the percentage of water drained.

Doing the calculation is very simple:


We can do this in parts in the installation to check if all those parts have the same% of drainage, which means that everything is in order, there are no problems with irrigation, obstruction of drippers or sprinklers, etc.

Irrigation provision

Irrigation is a very important (indispensable) variable in hydroponic cultivation and must be studied carefully. It will vary, of course, according to the crop and the substrate we use, since each plant has its needs and each substrate has its characteristics (retention capacity, porosity, drainage, etc.).

We must take into account what is the depletion fraction,  which means the maximum percentage of water that is lost through evaporation or drainage without negative effects on the plant, such as wilting. In the case of hydroponic cultivation, in most substrates, the depletion fraction is 5% and is a way to determine the separation and type of irrigation to be carried out.

Irrigation in period 1:

After a few hours of dawn, the substrate has a depletion fraction greater than 5% if it has not been watered at night, so it must be watered to regain adequate humidity levels. The amount of irrigation is measured by the percentage of drainage that is calculated from the previous formula, and in this period it must be between 5 and 10%.

Irrigation in period 2:

It corresponds to the hours of greatest solar radiation and, ultimately, of greatest heat. Relative humidity drops and has to be compensated by irrigation. The drainage levels must be higher but the irrigation frequency lower, reaching the case of having to carry out two irrigations in a period of less than 1 hour (some cases 30 min).

Irrigation in period 3:

It is the last hours of the day and about to get dark. The drainage level has to be reduced and corresponds to the moment when the water needs are quite low.

Irrigation in period 4:

Period 4 corresponds to the night, with the minimum levels of temperature and evapotranspiration. Normally it is not watered except for very hot times, since a good oxygenation of the roots is required. Drainage levels are between 10 and 25% at the beginning of the crop, and between 25 and 30% in its maturation stage.


NFT system

NGS system

And that’s it! We have left some things in the pipeline because hydroponic cultivation is a world, but little by little we will be completing sections with new articles that we are writing. All the best. Agromatic.

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