There are two levels of CO2 that are important:
1. minimal CO2 for growth at room temperature (perhaps "normal" ambient levels of 300 to 600 ppm)
2. nominal CO2-enriched levels of 1100 ppm for high-temperature (mid-80's to mid 90's F) growth, with added nutes, light, and water

I'll address only #1 above, since CO2-enrichment is an "advanced" technique I don't use yet:
The easiest way to provide CO2 is to ventilate your grow room to the outside air (from your house or from outside your house).
http://boards.cannabis.com/growroom-...-up-house.html
C02 concentrations in a home are only a bit higher than outside the home (unless you have something sucking-up the CO2, such as plants in your house somewhere). I figure that people and pets produce enough CO2 for a SMALL grow op (if you are only growing for yourself and a few people).

In other words, CO2 levels normally found in the home, and/or outside the home, are fine for growing.

If you do NOT ventilate, and are recirculating the air over and over, you'll eventually have to add CO2 only to keep it from dropping below, say 300 ppm. Without a C02 meter (which are expensive: $100's), you'll NEVER know if it drops too much, or goes too high. C02 concentrations above 1500 ppm are dangerous, and may hurt your plants.

Some folks suggest mixing baking soda/vinegar or sugar/yeast; or buying a "CO2 Boost Bucket" or CO2 "fizz" tabs/pucks. Perhaps burning a candle in your grow room every day or two may provide enough CO2, but who knows how much is too much? I'd hate to kill my plants this way. It's a lot of work to produce an unknown amount of C02 for a grow-room that started with an unknown C02 level, only to find out too much C02 hurt your plants.

I'd suggest ventilation as the only safe solution, and avoid C02 production unless you can buy or borrow a C02 meter.
search1st Reviewed by search1st on . What is the easiest way to provide sufficient CO2 to your plants? I've read up a little bit on it but it seems like none of the guides I'mn reading are straight forward. I just want to way you all have to say. Rating: 5