Sea Of Green, abbreviated SOG, is that you usually put between 16 to 25 plants few plants on 1 square metre. This commercial method of growing is mainly done by using slabs (hydroponic system).
Often plants are put on 12 hours light/12 hours of darkness schedule straight away, because they need to stay short and compact. Putting them straight away on a cycle of 12 hours of light and 12 hours of darkness can cause stress. Hence it is of paramount importance to have stable genetics that can cope with stress. More information: about sea of green set-up.