Cannabis plants need CO2 (carbon dioxide) to fuel photosynthesis. When you add CO2 to your indoor cannabis hydroponics grow room, you see faster growth and heavier harvests.

Ambient atmospheric CO2 concentration is 350-450 parts per million (ppm) and rising.  Regions with intense population density and/or polluting industries  often have intermittent “CO2 domes” floating on top of them that add CO2 and other air pollutants to urban air. Check with local air quality agencies about that.

You increase cannabis growth rate, health, harvest size, and potency by adding C02 to your cannabis grow room. Another benefit is that added CO2 in your gardening room enables your plants to handle more heat. Here’s how it works…

With only natural ambient levels of CO2, your ideal grow room temperature is 72-77°F, and especially during warm outdoor weather you spend a lot of money on air conditioning to maintain that temperature range.

But when you’ve added CO2, your cannabis plants better tolerate and may even thrive in temperatures as high as 86°F. You save money because you don’t have to keep the space so cool!

When you increase CO2 concentrations in grow room air, you must also proportionately feed your cannabis plants more hydroponics nutrients, more light, and more water. Your plants will tell you what they need. When you first start boosting C02, you’ll be surprised at how much added C02 increases plant metabolism to create thirstier, hungrier plants that want more light.

If you fail to increase nutrients, water and PPFD (photosynthetically active light) proportionate to C02 increase, the extra CO2 is wasted, or may hurt  instead of help your plants.

The only way to reliably, precisely add C02 to your grow room is get a tank of C02, and a regulator apparatus that connects to the tank to manage C02 outflow, along with a professional C02 monitor/controller. This is quite costly for initial start-up, and you have to return the tank and get refills periodically, which is a hassle and also costly.

Another C02-emitting device is called a burner—an appliance that burns propane or natural gas to create C02. These devices are very dangerous, hard to precisely control, and add unacceptable amounts of heat and humidity to the grow room.

You also see less-expensive products advertised for increasing grow room C02. Most of these products involve a bag or bucket with mushrooms, a fermenting material, or dry ice that allegedly emit small amounts of C02.

I’ve tested these products and repeatedly queried manufacturers of Exhale 365, C02 Boost, Pro C02, etc. The manufacturers refuse to provide any proof their products do anything other than generate profits for them. I consider them to be ripoffs—if their products actually worked well, they’d be more than happy to provide third-party scientific research proving it.

I’ve never seen these products add sufficient amounts of C02 to grow room air, and most growers finrally realize these items are a total waste of money.

Adding C02 to your indoor garden requires careful management and monitoring. I recommend using C02 monitors and controllers to automate delivery of C02 and keep it within ideal range, which is much easier than manually adjusting outflow valves. 

Some CO2 controllers are integrated with hydroponics climate controllers that monitor and adjust venting, fans, CO2 and other factors to ensure optimum temperature, air movement, humidity, CO2 levels.

Because C02 is heavier than air, some growers distribute their C02 from the top down. Given that most grow rooms and grow tents have aeration fans that mix the air anyway, I’m not sure this is necessary. You also see growers running narrow-gauge outflow tubing from their C02 unit that attach to plants near the top of the canopy. Again, not sure this is necessary or beneficial.

People growing in vented grow rooms must carefully time venting so it doesn’t remove added CO2 from the grow room, and it’s important to know you only boost C02 during lights-on hours.

The perfect C02 level for your grow room air depends on several factors, including lights-on temperature and vapor pressure deficit. In cooler grow rooms with temperatures below 77°F, and in grow phase, ambient C02 of 1000-1200 ppm boosts plant metabolism significantly.

In warmer grow rooms from 77-86°F and in bloom phase, C02 levels from 1200-1400 ppm will supercharge your plants.

Just remember, unless you upwardly increase other inputs such as nutrients, watering, PPFD, and keep vapor pressure deficit in range, your added C02 is mostly wasted.

I’ve seen C02 over 1400 damage plants, and CO2 above 450 ppm is bad for your health. It’s best to turn off C02 output and work in ambient, natural C02 environment when your garden needs tending. I’ve also known growers who turn off their tank C02 and do vigorous aerobic exercise in their grow room—their exhalations add C02 to the air.

Adding CO2 to your hydroponics cannabis grow room pays for itself and adds value to your cannabis cultivation, even with the costs of C02 equipment, and the extra light, water, and nutrients you use when adding C02 to grow room air. The payoff of adding C02 includes faster growth for more crop cycles per year, lower air conditioning costs, and heavier yields. It’s well worth your investment.