Of all the possible Hi-Tech methods to increase production and growth speed , in fact, the application of CO2 is certainly the quickest, simplest and most effective for hobby or industrial cultivation of indoor plants.

An increase in growth rate of 30-40% is typical for growing areas with high CO2 levels .

The absorption of CO2 for hemp plants , as well as for any other plant species, occurs through photosynthesis .

In this process, plants absorb carbon dioxide from the air and combine it with water using energy from light to produce sugars and oxygen.

An adequate supply of CO2, therefore, is also necessary for plants grown indoors to carry out the process of chlorophyll photosynthesis . 

A plant quickly absorbs the CO2 present in the air around it. If nothing is done to renew the air inside the cultivation environment, it will suffer from a lack of CO2 and will stop producing the sugars necessary for growth.

If, on the contrary, the air is moved, for example by a fan (which guarantees air recirculation) combined with an extractor (which instead guarantees its exchange), the plant grown indoors will have a greater and constant quantity of CO2 readily usable, and its growth will be more rapid and vigorous.

If then, in addition to a good ventilation/extraction system, CO2 is added in large quantities, the indoor plant will respond with a huge increase in growth speed.

In this practical guide we will focus on this aspect, that is, on use

of CO2 in indoor growing. 

What do plants use co2 for?

CO2 for legal cannabis plants and other indoor grown plants is essential . But, often, growers do not take into account the lack of CO2 in grow rooms as this can negatively impact the final yield. Often those who grow indoors with grow tents make the serious mistake of extracting the air, "recirculating it in the same environment with the windows closed. 

After a few hours, this expedient creates an environment rich in oxygen, but almost devoid of CO2, causing significant slowdowns in growth. To avoid this, the ventilation ducts connected to the aspirator must necessarily expel the air outside;

Indoor plants in the vegetative growth phase rapidly use the CO2 present in the cultivation environment, replacing it just as quickly with oxygen.

When indoor plants have consumed about a third of the CO2 present, especially in the case of large or rapidly growing plants, their development will visibly slow down. 

The situation becomes more serious in Grow tents where there is no fan to create internal air recirculation , this is because in the absence of recirculation a sort of microclimate is created around the leaves.

The small portion of air around the leaves quickly becomes very low in CO2 and even if there were adequate levels of carbon dioxide around the leaves themselves, they would not be in direct contact with air containing enough CO2.

Installing a CO2 kit for indoor growing can prove very useful, even in grow tents  with good internal recirculation. This is because, in a closed room full of plants in the vegetative phase and in good health, the CO2 present is consumed in less than an hour.

Before continuing to talk to you about how to best use carbon dioxide in an indoor growing, we want to focus on another vitally important aspect: how to measure the value of CO2 present in your Grow Room.

the importance of CO2 for plants: how to calculate carbon dioxide in your indoor growing

The CO2 measurement is calculated in Parts Per Million (ppm) . For example: country air contains around 300 PPM, while in the city the level rises to at least 400 PPM.

Many researches tell us that the ideal level of carbon dioxide present in the air, to obtain a concrete increase in the speed of growth, is around 1500 PPM , i.e. approximately 4 times the level of CO2 present in the air we are used to breathing. 

For example, milligram (mg) can be expressed as 1 ppm compared to 1 Kg which represents 1 million milligrams (1000000 mg = 1 Kg). 

So if I am measuring the concentration of an element within a kilogram of any material and I find a value equal to 3 mg of impurity, I can read it as 3 ppm but only relative to 1 Kg.

This also applies to volumes, for example the microliter [0.000001] corresponds to 1 ppm of a liter.

To measure how much carbon dioxide there is within your cultivation area, there are different types of environmental CO2 meters on the market , which are very precise and reliable in returning the measured values.

However, there is no way to calculate how long it takes for CO2 to be added. Consumption by plants also depends a lot on ventilation, for example. The ideal would be to constantly monitor the value and guarantee a daily refreshment of CO2, especially during the flowering phase.

Before choosing a kit for the production of CO2 , always remember that carbon dioxide is only one of the different and interdependent factors that contribute to the increase and speeding up of growth, namely:

  • Ventilation;
  • Temperature;
  • Humidity;

If any of these factors are forgotten or ignored all your efforts with CO2 will have been in vain.

In the next paragraphs we will also carefully analyze these aspects and how to maintain an optimal level of carbon dioxide if you grow legal cannabis or other plant species indoors.

The importance of temperature and humidity with supplentary co2 for plants

Like the concentration of carbon dioxide, temperature and humidity are also key factors for the good growth of indoor plants.

If these 3 factors are not in balance, in fact, there is the risk that the plant will not grow well or that it may be more susceptible to mold and diseases.

Temperature and relative humidity must be constantly measured with a digital thermo-hygrometer , the optimal ranges are:

  • Temperature of 30-35°C (in case of addition of CO2 indoors): , below 30°C if carbon dioxide is not added;
  • Relative humidity 40-65%.

According to some experiments, the maximum increase in growth speed occurs around 35°C, in the presence of 1300-1500 PPM of CO2.

Other studies claim, however, that the addition of CO2 leads to a practically zero increase in growth speed if the temperature is below 24°.

The maximum value of 65% humidity must never be exceeded, especially in the flowering/fruiting phase, but problems can arise even around 60%. In fact, many fungi are unable to develop with lower relative humidity and in the presence of vigorous air circulation.

Often, increased humidity is overlooked during the dark period. However, the hours of darkness are the ideal period for mold to develop.

Therefore, it is a good rule to keep the ventilation on during the dark hours to avoid the onset of mould, making sure, however, that the external temperatures are not below 12°.

A good method to keep the temperature constant and humidity low during the dark hours is to use a small dehumidifier in the growing environment.

Keep in mind that as the temperature drops, the humidity increases. In fact, the warmer the air, it has a greater capacity to contain humidity. The same amount of water dissolved in cold air creates more humidity in indoor CO2 grows.

Autoflowering plants and indoor cultivation: what is the ideal maximum temperature

When growing autoflowering plants and other plant species indoors, the heat generated by using HPS or MH lamps can create considerable problems for the grower.

In fact, it may be difficult to maintain the temperature below 26°C if you do not add CO2 or below 35°C otherwise, especially during the summer.

Personally, we believe it is essential to use:

In fact, the Cooltube makes it possible to suck in the air present in the immediate vicinity of the HPS lamp and therefore also most of the heat produced by it.

In this way, it will be possible to position the lamp much closer to the plants (max approximately 20 cm versus 50/60 cm if the Cooltube is not used) and to maintain the CO2 within the cultivation area, and the desired temperature.

From some tests carried out, we have unequivocally demonstrated that this is true. Having a Grow Box available which consists of a wardrobe with a base of 70x100 cm and a height of 200 cm:

  • The HPS 400w lamp was positioned inside (without Cooltube) but with the extractor (280 m3) and fan working: after an hour it recorded a temperature of around 35°C;
  • Once the Cooltube was applied, all other conditions being equal, the temperature remained, again after an hour, at 21°C. 

The experiment was carried out in December. Now, it is clear that 14°C passes between 35°C and 21°C. 

And it is equally clear that, by equipping the air extractor (connected to the Cooltube) with a timer that allows you to adjust its On/Off, you can, starting from one of the two extremes, for example "always on" (21°), program increasingly longer shutdown intervals to raise the temperature until reaching, hypothetically, the opposite extreme of "always off" (35°). 

Obviously it must be considered that in the event of intervals of switching off of the air extractor, when it is switched off, the Cooltube does not carry out its function, therefore it is not advisable to position the lamp too close to the plants (i.e. 20 cm, maintain a distance of at least 30 or better 40 cm).

What is the ideal humidity in a co2 grow tent

Many growers are able to solve the problem of controlling humidity in the CO2-added grow box without resorting to electric dehumidifiers, which consume a lot of electricity.

There are two very simple actions to carry out to avoid the accumulation of humidity in the cultivation air:

  1. Increase air extraction, given that generally the humidity outside the greenhouse is lower than inside;
  2. Increase internal recirculation.

The problem can be solved with a good extraction/ventilation system for the greenhouse, which is certainly less expensive both in terms of expense and electricity consumption than using an electric dehumidifier. 

Supplementary CO2 for cannabis plants: how to maintain optimal co2 levels in a grow tent

If CO2 is added without adequate air circulation in the Grow Room, the substance immediately precipitates to the roots of the plants (as it has molecules heavier than those of oxygen). Even if the ventilation is too mild, it is unable to reach leaves.

The secret to maintaining optimal CO2 levels in the grow tent lies in internal air recirculation . Simply put, the most productive grow tents are the best ventilated ones. For what reason?

Indoor plants seem to benefit from the constant presence of high levels of CO2 in the air. Furthermore, the constant movement of indoor plants due to fans causes tiny tears in the tissues which contribute to the formation of shorter stems:

  • Strong;
  • Vigorous;
  • Robust.

Suitable, therefore, to support the weight of the abundant flowering/fruiting that is obtained by applying HI-Tech cultivation techniques.

Some growers use a double ventilation system : powerful oscillating fans are placed above the plants while a second fan system is applied below them, which guarantees constant and vigorous recirculation.

Internal recirculation , by means of an air extractor , is obviously also necessary during the addition of CO2 .

In this way, as already mentioned, the depletion of CO2 in the air near the leaves is avoided and also disperses any emissions of hormones and other chemical substances into the air by the plants.

If CO2 is added, periodic total air exchange is desirable, if CO2 is not added, it is essential to ventilate and extract the air continuously.

How to create co2 for plants?

The answer is simple. With a special kit that allows the production of carbon dioxide within indoor crops.

The kits for adding CO2 are usually composed of:

  • CO2 cylinder;
  • Pressure reducer;
  • Pressure gauge with regulating valve;
  • Solenoid valve that closes and opens the system;
  • Digital timer.

The administration of carbon dioxide can also take place using CO2 Box dispensing bags and CO2 tablets for effervescent and slow-release plants, particularly suitable for hydroponic cultivation.

Visit our category on CO2 and make sure you guarantee your legal cannabis plants and other plant species the right dose of this substance so important for their growth.