If you are green to gardening you might not know that carbon dioxide, the gas we all exhale, is critical to plant growth and development. Photosynthesis, the process through which plants use light to create food, requires carbon dioxide. CO2 concentration in ambient air ranges from 300-500 parts per million (ppm), with a global atmospheric average of about 400 ppm. If you are growing in a greenhouse or indoors, the CO2 levels will be reduced as the plants use it up during photosynthesis. Increasing the CO2 levels in these environments is essential for good results. Additionally, there are benefits to raising the CO2 level higher than the global average, up to 1500 ppm. With CO2 maintained at this level, yields can be increased by as much as 30%!

Commercial greenhouses are aware of this and commonly use CO2 generators to maximize production. One thing to keep in mind while designing a CO2 system is that yields will only increase if CO2 is your ‘limiting factor’ (for more on ‘limiting factors’ and ‘Leibig’s Barrel’, see our previous post here). This means that if all your other variables are not optimal (light, fertilizer, temp/humidity, pH, etc.) you will not achieve the benefits of increased CO2 levels.

Now that we know the benefit of adding CO2 to your indoor growing environment, one thing to note is that CO2 enrichment will not be as effective if your grow area is not sealed since it will be exhausted before the plants can use it. Ideally, air should not be exchanged in an out of your grow room. If you have an air-cooled reflector, the air drawn through the fan to cool the bulb must enter and exit the grow area without coming in contact with the air in the grow room. Sealing your grow space allows plants to more completely use the CO2 that you enrich the environment with.

Another thing to note is that during the night cycle plants actually give off CO2. This causes a gradual increase during the night, until the lights come on and the plants resume absorbing CO2; you can save CO2 by waiting an hour or so into your daylight cycle to cut your CO2 device on.

Lastly, CO2 is notably heavier than air, so it is essential that your CO2 be dispensed from above your plant canopy. Oscillating fans in the grow space, particularly around the CO2 dispensed, will help distribute the CO2 around the area.

Now, let’s look at the various ways you can increase CO2 levels:

Homegrown CO2’s Exhale bags are a great option if you would like to see what CO2 can do for your garden on a budget and without a lot of equipment (i.e. timers, regulators and monitors). Exhale bags are filled with mycelium (non-fruiting mushrooms) that give off steady amounts of CO2 as a byproduct of their metabolism. These bags end up costing less and can save you a ton of hassle compared to the infamous fermentation and dry ice methods. For $32.99 you can buy an Exhale bag (available in-store only) that covers a 4×4 area for 6 months. After hanging your Exhale bag above the canopy you can use a CO2 test kit to see how much it raises CO2 levels.

If you are ready to move up to a longer term, more efficient CO2 delivery system, then the next system involves using a pin timer (Apollo 8), a CO2 regulator and either a CO2 tank (available for purchase or refill) or a CO2 generator. Tanks are typically the better option for smaller spaces for ease of use whereas generators tend to be the better option for larger spaces since they run off of propane and can generate large volumes of CO2 at low cost. Now, with either source, set the pin timer to turn the regulator on for 15 minutes every 90 minutes or so. A CO2 calculator like this one, available from Greentrees Hydroponics, will help you determine how much CO2 you need to release to achieve optimal concentrations for plant growth. You can also use a CO2 test kit to dial in your system so that 1500ppm level is maintained. As your plants grow and the garden changes, retesting your CO2 levels monthly can help you tweak your system to maintain optimum levels. Note, if you are using a Titan CO2 Regulator, a ¼” dispensing tube is included. Hang this line above your canopy in a circle with small holes every couple of inches (to allow the CO2 to ‘rain’).

Finally, for gardeners that want to achieve constant optimal growth conditions without ever wasting extra CO2, a CO2 monitor is a great device. These monitors, such as the Titan Atlas-3, completely automate your CO2 system by constantly measuring the CO2 in the area. If the ppm level falls lower than what you set on the monitor, it will automatically open the regulator and dispense CO2. These monitors also come equipped with a photocell to ensure that you never dispense CO2 during the night cycle.

By: Chase Werner

Useful Resources:

CO2 Calculator – This is a great tool to use to make an intelligent first calibration of what your requirements will be for your room size instead of guessing and checking.