Honestly? I can't say if it made much of a difference, the plants I have outside in mother nature have already outgrown my indoor spring crop and they have two+ more months of good vegatative growth left and will easily be double the size they are now. Dry ice works too but it's expensive an inefficient. I think if you grew one or two plants in a closet and put 3-4 bottles of yeast/sugar water you'd help the plant but it takes a lot to double the natural amount of co2 in the atmosphere. Theory is that once upon a time there was actually more co2 in the atmosphere and thats why plants thrived so well during the dinosaur ages.