The greatest advantage of indoor horticulture is having ultimate control over light cycles, nutrition, and atmospheric conditions. A grower should do everything in his or her power to make sure their growroom’s lighting, nutrition, temperature, and humidity are precise and consistent. After all, it is only when a plant has access to sufficient light and balanced nutrients, and is provided with the appropriate atmospheric conditions, that it will be able to achieve its full potential.

Once an indoor horticulturist dials in these crucial factors, however, he or she can take the next step toward maximizing the garden’s productivity. This can be done by supplementing CO2 into the garden’s atmosphere. Higher levels of CO22 have been shown to significantly increase plants’ growth rates and, therefore, the garden’s yield. On average, ambient air has around 350-450 ppm of CO2 (it can be greater in urban areas with more air pollution). A grower who wishes to gain all the benefits associated with enriched CO2 levels will typically increase CO2 levels to 1,000-1,500 ppm. This enrichment can be achieved by a few different methods combined with specialized CO2 control devices.

CO2 and Photosynthesis

Plants are unique creatures because they can directly convert light energy into usable energy for growth. This phenomenon is known as photosynthesis, which can be using the chemical equation:

6CO2 + 6H2O + light energy = C6H12O6 + 6O2.

In the first part of the equation, there is CO2 (carbon dioxide) and H2O (water). When plants have access to these compounds in addition to light energy, they can produce the second part of the equation: C6H12O6 (glucose) and O2 (oxygen).

It may look and sound complicated, but don’t be alarmed; you do not need a degree in chemistry to be a successful grower. Still, it is important to note that photosynthesis is a chemical reaction. Like other chemical reactions, photosynthesis can be affected by factors like temperature and access to the proper chemical compounds.

One of these crucial chemical compounds is CO2. Plants absorb carbon dioxide through the open stomata on their leaves. Transpiration, which helps keep plants at an even temperature, occurs when the stomata are open as well. However, transpiration results in the loss of water (another significant chemical compound for photosynthesis); so, to conserve water, plants regulate the amount of time the stomata are open.

When a grower enriches the environment with CO2, however, the amount of CO2 available for absorption increases for the length of time the stomata are open. In other words, the plant can absorb more CO2 while still limiting water loss through transpiration. Some experiments have also shown that when provided with an increased amount of CO2, plants will not open the stomata as wide, thus reducing the amount of transpiration. All in all, increased CO2 levels will increase the efficiency of a plant’s water use. Assuming the plant has access to the necessary nutrients and light energy, the additional CO2 absorbed, combined with the increased efficiency of water use, will increase the plant’s rate of growth.

Methods Used for CO2 Enrichment

There are a few different ways to increase the level of CO2 in the garden. For large spaces, the preferred method is generally a burner. CO2 burners are fueled by propane or natural gas. As the fuel is burned, CO2 is created as a by-product of the combustion. There are many different burners available and the size required generally depends on how large of an area a gardener is trying to enrich. Unfortunately, these devices also create heat in addition to creating CO2. This is usually viewed as a disadvantage of CO2 burners because most growers work hard to remove unwanted heat that is created by the intense lighting systems. Still, in commercial gardens or in very large growing facilities, burners are the most effective way to produce the large amount of CO2 necessary to enrich the environment.

Another common way to increase CO2 levels is to use pure CO2 contained in a tank or cylinder. This method of enrichment utilizes containers of compressed CO2 teamed with a CO2 emitter. The emitter regulates the rate at which the CO2 is released from the tank and is normally combined with a timer or controller to determine when the CO2 should be released. A compressed tank system is a great choice for many hobby growers because it is not only effective at increasing CO2 levels, but also will not create additional heat in the garden’s environment.

The final method of CO2 enrichment commonly used by indoor horticulturists is mycelium-based CO2 systems. These devices can be purchased in buckets, bags, bottles, boxes, or mats, all of which contain strains of fungus combined with a food source for that fungus. As the fungus creates its mycelium (its equivalent to the vegetative process), it releases CO2 as a by-product. This type of CO2 enrichment is great for small areas, such as closets or small bedrooms. They are also relatively inexpensive, which allows a grower to experiment with CO2 enrichment without making a huge investment.

Controlling CO2 Consistency

A grower should team a CO2 device with some sort of controller so the emission rate of CO2 can be regulated (mycelium-based CO2 products are the exception as they can’t be controlled). Using automation devices that control the level of CO2 within the room is imperative to both the efficiency and the effectiveness of the CO2 system. Many atmospheric controllers come equipped with built-in CO2 control systems. There are also stand-alone CO2 control systems available.

A good CO2 controller will essentially automate the CO2 system, controlling both the concentration (usually expressed in ppm) and the appropriate times for operation. Plants thrive in consistent environmental conditions and the concentration of CO2 is no exception. The amount of CO2 in the environment is detected by a “sniffer”, which will periodically sample the atmosphere’s concentration of CO2 and send a signal to the controller. If the concentration falls below the system’s set-point, the controller will then trigger the CO2 device to turn on. On the other hand, a good controller will stop the CO2 unit when exhaust fans are in operation so the CO2 is not being removed from the garden as soon as it is emitted. Newer, software-based control systems offer additional control features, such as remote access to the devices and data logging. Data logging of CO2 levels can provide valuable information over the course of a few garden cycles and can help a gardener determine the optimal concentration of CO2 for their particular crop.

Temperature and Nutrient Requirements for CO2 Enriched Environments

As previously mentioned, photosynthesis is a chemical reaction and, like other chemical reactions, it can be affected by temperature. A typical indoor garden will have an optimal temperature range of 70-80˚F. The optimal temperature of an indoor garden enriched with CO2 will have a slightly higher optimal temperature range (usually around 75-85˚F).

It is also common for growers to increase the nutrient concentration in growrooms with increased CO2 levels. This makes perfect sense because if the rate of growth increases, the nutrient requirements will increase as well. Since each plant varieties’ nutrient requirements are unique, there is no perfect way to tell the exact nutrient concentration needed. That being said, a grower can expect to increase his or her garden’s nutrient concentration by five to 15 per cent when enriching the atmosphere with CO2.

Increasing the amount of CO2 in the atmosphere of an indoor garden or greenhouse can increase growth rates when all other factors are considered. This will not only equate to faster vegetative growth, but also larger yields. For some growers, increasing the rate of vegetative growth will allow them to start fruiting or flowering more quickly. A shorter vegetative cycle can mean more garden cycles per year—a more profitable garden.

Growers who want to invest in CO2 equipment should go all-in. In order to reach the full potential of a CO2 enriched environment, growers will not only need equipment for creating the CO2, but also the adequate control devices to automate the system for efficiency. Without the full package, CO2 enrichment can be a disappointing venture with little gained in terms of overall financial investment.

CO2 enrichment should be viewed as icing on the cake. In other words, CO2 systems should be something that growers add to an already fully functional and productive garden. The basics of lighting, ventilation, and nutrition should always be the first priorities for any indoor grower striving for success.