Carbon dioxide (CO2) bags are a low-cost, passive method for hobbyist growers to increase plant growth and yield in controlled environments. Plants require CO2 for photosynthesis, the process that converts light and water into the energy necessary for life. Increasing the concentration of this gas above the ambient atmospheric level of about 400 parts per million (ppm) can accelerate growth. This method is often touted as a simple alternative to complex equipment, leading many to question its measurable results in a typical indoor setup.
How CO2 Bags Generate Gas
Commercial CO2 bags primarily utilize a biological process to generate the gas through microbial respiration. These systems contain a substrate, often composed of organic materials, inoculated with a living culture, typically a fungus or mycelium. As the mycelium consumes the organic matter, it respires, releasing CO2 as a byproduct.
There are also some chemical CO2 products, but the biological bags are more common in the slow-release market. The output from mycelium-based bags is entirely passive and continuous, relying on the metabolic activity of the fungus. This means the rate of CO2 release is slow, non-adjustable, and typically lasts for several weeks to a few months.
When CO2 Bags Are Effective
For plants to fully utilize supplemental CO2, the growing environment must be optimized in several ways. The benefits of CO2 enrichment are only realized when the plants are grown under high-intensity lighting, which often requires a corresponding increase in temperature. Most crops reach their saturation point for CO2 between 1,000 and 1,300 ppm, a level significantly higher than normal air.
The effectiveness of CO2 bags hinges on the environment being sealed or having minimal ventilation. Because the gas is released slowly and passively, any significant air exchange will cause the enriched CO2 to be vented out almost immediately. In a typical grow tent or room where exhaust fans run frequently, the concentration may never rise high enough to make a difference. Bags are generally only effective in very small, fully enclosed spaces, such as micro-tents, where the natural CO2 is quickly depleted by the plants.
Practical Placement and Circulation Needs
Carbon dioxide is denser and heavier than the surrounding air, meaning it will naturally sink toward the floor of the grow space. For this reason, the CO2 bag should be placed or hung slightly above the top of the plant canopy. This allows the released gas to cascade down over the leaves, where the stomata can absorb it.
To prevent the CO2 from simply settling on the floor, internal air circulation is necessary. Oscillating fans positioned inside the sealed growing area must gently mix the air to distribute the gas evenly throughout the canopy. Without this constant movement, the higher CO2 concentration remains only in the bottom layer of the room, failing to reach the upper plant portions most exposed to light. The goal is to ensure the slow, consistent stream of gas is constantly swept over the plant leaves.
CO2 Bags Versus Pressurized Systems
The choice between a CO2 bag and a pressurized delivery system centers on cost, control, and consistency. CO2 bags are inexpensive, require zero maintenance, and are easy for a beginner to set up. However, they offer no control over the concentration level or the timing of the release.
Pressurized systems use tanks of compressed CO2 and automated regulators. These systems are significantly more expensive but provide precise control. They allow a grower to consistently hit the optimal target range of 1,200 to 1,500 ppm and only release the gas when the lights are on. While bags are a low-risk, low-cost option best suited for small, sealed environments, pressurized systems are the only way to reliably achieve and maintain the high CO2 levels required for maximum yield increases.