Nico’s Nuggets: CO2 In Small Gardens

Question from: SoCalGrower42

Hello, Nico. I’m a huge fan of your work and want to thank you for all the articles and videos over the years! My question concerns CO2 and acceptable levels for indoor gardens. My room is small, about 10’ x 10’. How much CO2 is too much, or is there no such thing as too much?

Greetings to you, SoCalGrower! Thanks for the kind words and for writing in! Your question is an excellent one, as there are many myths out there about CO2.

To begin with, I always remind people that huge amounts of CO2 are not necessary to grow high-quality marijuana. While CO2 is an integral part of a plant’s physiological and biological processes, added CO2 does not necessarily equal high potency or more flavor. If anything, CO2 is more for packing on weight and is a way for commercial growers to significantly increase yields.

Now that’s not to say that a small home-grower such as yourself shouldn’t use CO2, but there is a point of diminishing returns – especially for smaller growers like you. Ambient levels of CO2 in urban areas usually range between 400-500 PPM (parts per million). Growers who bump this up to 800-1000 PPM are well-advised to do so. I’m not usually a big fan of a lot of CO2 as I feel that the added cellular production detracts from the resin and terpenoid production within the plant. Some growers may not feel the same, though.

To be honest, studies on vegetables have shown that plants can handle upwards of 10,000 PPM of CO2 with little to no ill effects (though I wonder how those huge tomatoes taste). However, at high light densities – which we produce with our indoor lighting set-ups and HID lamps – indoor plants have a maximum CO2 uptake of closer to 2500 PPM. This is due to heat’s effect on photosynthesis. Once a garden temperature reaches 86 F, CO2 use should be shut down.

Additionally, it is important for indoor growers to remember that specialized atmospheric controllers should be used for indoor gardens that have automated venting or cooling systems. The last thing you want is your exhaust fans going on while your CO2 tanks or burners are going. For smaller indoor gardens such as a bedroom or large closet or attic space, there are cheaper more passive CO2 solutions such as a CO2 Boost bucket, which utilizes decaying compost to boost CO2 levels a few hundred PPM (and are eco-friendly and inexpensive!). Barring that, small CO2 tanks can also be utilized with regulators and timers. The bigger propane burners are generally reserved for larger, commercial operations.

Thanks for reading everyone and remember: Grow… And help the world grow, too!