Grow Room CO2 on a Timer

Using the timer method with CO2 tanks, what is the recommended cycle for boosting the levels? 4 times a day? 5 times a day? I have a 5x5 grow tent.

Answer: The answer to your CO2 question depends on several things. First, the volume of your grow room. You have only given me two dimensions of your grow room, 5' (long) and 5' (wide), which is enough to calculate area....but not enough information to figure out the volume of the space. To figure out the air volume of your garden, I would also need a third dimension (height).

The next factor that will affect my answer is how frequently you are running your exhaust cycles. Every time you exhaust your grow room (to keep the temperature from getting too high), you also exhaust all of the CO2 rich air. Therefore, each time you run an exhaust cycle, you need to follow it by running a CO2 cycle. How long you leave the CO2 on during this cycle is a math problem, requiring you to know the volume of the grow room, the flow rate that you have your CO2 regulator set to, and the level of CO2 supplementation you desire to bring your garden up to (such as 1,500 ppm or 2,000 ppm). On my Using CO2 page, I walk you through all of this step by step.

Having a lot of experience trying to grow things in small spaces under grow lights, I have a pretty good idea how this is going to go for you. You will set up your grow room and quickly realize that you need to keep your exhaust fan running all the time just to keep the space livable (but probably still too warm) for your plants. At that point, you will have two options....either add air conditioning and run the exhaust to cool your light completely separate from the the air in the rest of the grow room, or else release your CO2 constantly (but slowly) as you are exhausting the room constantly.

Adding air conditioning with the CO2 is the best option, but in reality you do have a third option. For gardens tucked into small spaces and constantly exhausting, I often recommend no CO2 supplementation. First, there is usually a temperature issue....if all of the plant growth factors are not kept ideal, than you will not even realize the benefits of adding CO2 when it comes to the weight of your harvest. No sense in spending all that extra money setting up a CO2 system if you are not going to realize substantial gains from the strategy.

Second, plant growth will only stop if the atmospheric CO2 levels drop below 250 ppm (normal levels in the atmosphere are about 400 ppm). If you are constantly exhausting the grow room and constantly bringing in fresh air to replace it, you will never have an issue with having too little CO2 in the air.

Read this carefully and follow the links, especially the one for my CO2 page (it has a great section on CO2 calculations and setting timers), and you will have all the answers you are looking for. Just for good measure, also check out the exhaust setup page to brush up on the best strategies for exhausting your grow room area. I hope this helps, and Happy Growing!