CO₂ enrichment

Since outdoors air CO₂ level varies in the 400-700 ppm range at any time and most plants grow better in the 700-1500 ppm range, there is a gap to fill. CO₂ concentration enrichment aims at filling the gap to raise the limit to plants growth rate.

Good climate control needed!

Before to engage in CO₂ enrichment, the gardener has to well control all other growth variables to maintain plants'stomas opened 24 hours a day. Getting above average yields by well controlling lighting, watering, air temperature and humidity is required. Without proper control of the atmosphere, CO₂ level enhancement will not promote efficient photosynthesis and deliver all the potential benefits.

Raising the CO₂ level may also require some garden climate control adjustments to avoid venting this precious plant food out of the garden. A good coordination between ventilation and CO₂ enrichment is a must. Since ventilation is often used to cool and dehumidify the garden and bring in some fresh needed oxygen, its control has to be coordinated with CO₂ enhancement. When feasible, ventilation should only work a few minutes per hour to replenish the oxygen level.

For example, a CO₂ combustion generator (Figure 1) releases heath, CO₂ and water vapour. The extra heat raises the garden temperature. The extra water vapour raises the humidity level. The use of a CO₂ combustion generator may require the installation of an air conditioning unit or other cooling equipment and a dehumidifier. If the intake-exhaust fan(s) operate at the same time, some CO₂ is thrown out. In a well balanced garden climate, a combustion generator should not work more than 10 to 12 minutes per hour. It requires about 2 to 5 minutes ventilation to replenish the oxygen needed for a clean risk-free combustion: insufficient oxygen supply for combustion may produce carbon monoxide toxic to humans and ethylene toxic to plants.

Figure 1: LEFT: Plug'N'Grow CO₂ combustion generator; RIGHT: with a clean equipment and proper oxygen supply a CO₂ combustion generator produces mainly blue flames from propane (LP) or natural gas. A CO₂ combustion generator needs periodic maintenance like cleaning the core of the burner jets.

The bottled CO₂ regulator (Figure 2) is another device to enhance CO₂ concentration: it does not increase the indoor temperature, nor adds to humidity and no oxygen is depleted in the CO₂ release process. On the cons side, heavy CO₂ bottles have to frequently be refilled and transported.

Figure 2 : LEFT : A common CO₂ regulator setup: an electric solenoid valve is actuated to release the CO₂ gas in the garden's atmosphere. RIGHT : The Plug'N'Grow high capacity CO₂ regulator iGS-REG

There are other methods and supplies to enhance CO₂ level in a garden. Although cheaper than the CO₂ combustion generator and the bottled CO₂ regulator, they are difficult if not impossible to control, may emit CO₂ in the dark when unneeded or raise concentration to useless level. A programmable timer may also be used to control a CO₂ regulator as shown in Figure 2 LEFT: this type of control is cheap and difficult to adjust in order to get the right CO₂ level and avoid waste as it is not coordinated with the intake-exhaust fans.

Precise control for better results and to avoid waste

Both the CO₂ combustion generator and the bottled CO₂ regulator can be accurately controlled to enhance the carbon dioxide level at the proper concentration for the plants needs. This is generally accomplished by means of a CO₂ ppm (parts per million) environmental controller (Figure 3). The CO₂ ppm controller allows for a photoperiod setting to enhance concentration to the proper level while avoiding combustible or bottled CO₂ waste. Having a digital display of the current CO₂ level, the ppm controller also acts as a warning device. Entering the garden and looking at the controller display tells the gardener if he is at risk of CO₂ intoxication and if the enhancement equipment is in good working condition.

Figure 3: LEFT : A combined CO₂, temperature and humidity controller able to manage 6 equipments and coordinate minimal essentiel ventilation. RIGHT : A stand alone CO₂ controller best used when the garden is cooled by an air conditionning unit.

To increase the CO₂ concentration in the garden's air, combine a CO₂ PPM control with either of :

CO₂ Combustion Generator using liquid propane or natural gas

Bottled CO₂ Regulator