Why is light deprivation so important to greenhouse Cannabis growth?  

The ability to control the timing of your plants 24hr light cycle is key to making your cannabis flower. Cannabis in vegetative growth requires more light than dark so a 18hr/6hr light to dark cycle can help achieve natural big growth before flowering.  When the lighting cycle is changed to 12hr/12hr the plants, believing it is late summer, will start to produce flower. Light deprivation is key in allowing greenhouse growers to control light cycles throughout the year in order to achieve multiple harvests.