The dark cycle is very important to growing marijuana. Respiration ( this is when the marijuana plants are making energy from sugar and oxygen) continues in the dark period but at a much slower rate, almost independent of available oxygen because the leaves of the weed are not making oxygen in the dark.

In the dark, there is a shift from leaf production to root production as the leaves transfer excess stored energy down to the branches and to the roots. Therefore, some dark time allows for better root structures.

Another article will be written on why a 24-hour light cycle is not the way to supercharge root growth of your marijuana plants.