In enclosed grows with special lights, micro-nutrients, and growing mediums. Marijuana plants can use more than the 350ppm of CO2 available in normal air. The normal growth rate of a Marijuana plant under these conditions will increase with CO2 enrichment and cut down on growing times and increase yields.
You can introduce CO2 into your grow at anytime during the vegetative or flowering process. As soon as CO2 is introduced the growth rate will increase. The CO2 is only used while the lights are on so there is no need for CO2 enrichment while the plants are in the dark. CO2 is only useful to the Marijuana plant for growing tissue-material and is not needed for resin production or the production of THC. It is highly suggested that the CO2 enrichment process be stopped during the last 2-3 weeks of flowering when the plants put more of their energy into THC and resin production rather than new tissue growth. Some growers even say that the use of CO2 during these last few weeks lowers the THC, resin production, and reduces potency so to be safe I would suggest stopping the enrichment process during this last few weeks.
I have read several articles and forum threads on the subject of using CO2 for growing marijuana indoors or in a closet. I finally came to the conclusion after testing a CO2 tanks hooked up to my smaller closet grow operation that it really all depends on the growing set-up. Here are a couple of scenarios:
Using CO2 In A Perpetual Closet Grow Area
Using CO2 In A Perpetual Room Grow Area
A perpetual room grow is considered to be a grow operation that has multiple rooms and is continuously in operation. One room for vegetative growth, one room for flowering, and a small area for rooting clones. In this scenario, if you have enough light and height to allow your plants to grow fast and tall or big and bushy, then I say go for it. Take advantage of introducing CO2 to induce a faster more robust growth rate, increase your yield and make for a healthier plant!
Using CO2 In A Single Grow Area
A single grow is considered to be a room where your plants go through the vegetative growth stage and the flowering stage without being moved. In this scenario it would be a good idea to use CO2 seeing as you want the plants to grow as fast as they can in the vegetative growth stage so you can switch them to 12/12 and start the flowering process sooner. You’ll be able to gauge your height and switch the lights to 12/12 before your plants out grow your room. In this case you may be able to cut a week or maybe two off your grow time.
So you see it all depends on the grow area and what the time constraint or height constraints are.. timing is everything when trying to grow continuous crops and the introduction of CO2 in certain grows would throw the times off between vegetative growth and the flowering stage. Basically it all depends on the scenario. It is a good thing to enrich your grow with CO2 as long as the increase in growth rate doesn’t mess things up and the CO2 is not used in the last few weeks of flowering – potentially lowering THC-Resin production and potency.