Composted CO2 - A compost heap is a pile of decaying matter such as leaves, twigs, plant clippings, etc. Large amounts of CO2 are released during the process through fermentation. A good compost turns 100 pounds (wet weight) of organic material such as leaves or plant trimmings into 50 pounds or more of CO2. The fermentation process takes about a month, and releases CO2 in fairly regular daily amounts once the digesting action begins (great for cannabis seeds plants). Starting a compost in a grow room would be a very messy and unsanitary proposition, but there are probably several “country” applications wherein a compost system could supply clean and adequate CO2 to a cannabis greenhouse or larger growing cannabis operation.