The question of whether an autoflowering cannabis plant can be grown using a 12 hours of light and 12 hours of darkness (12/12) cycle is common among new cultivators. This 12/12 schedule is the standard method used to trigger flowering in photoperiod cannabis strains by simulating the shorter daylight hours of autumn. Autoflowers, however, possess unique genetic programming that makes them fundamentally different from their photoperiod counterparts. Understanding this difference is key to determining the ideal growing environment for these rapid-cycling plants.
Understanding Autoflower Genetics
Autoflowering cannabis strains owe their unique life cycle to the inclusion of genetics from Cannabis ruderalis, a wild subspecies native to regions with short, cool summers. Unlike Cannabis indica or Cannabis sativa, the ruderalis genetic makeup evolved to initiate flowering based on the plant’s age or maturity rather than the photoperiod. This internal clock ensures the plant can complete its entire life cycle quickly before the onset of harsh winter conditions.
This means autoflowers do not possess the same photoreceptor mechanisms that allow photoperiod plants to measure hours of continuous darkness to trigger the bloom phase. Instead, they will automatically transition from the vegetative stage to the flowering stage, typically within two to four weeks of germination, regardless of the light schedule they receive. This built-in autonomy is what gives autoflowers their name and allows them to be much more flexible in their light requirements.
The Direct Answer: Viability of 12/12
The straightforward answer is yes; autoflowers will still flower and produce a harvest on a 12/12 light schedule. Since flowering is determined by an internal timer based on age, the reduced light hours will not prevent the blooming process from starting or finishing. The plant will begin to develop flowers once it reaches maturity, typically 21 to 30 days after sprouting.
The 12/12 schedule will not delay flowering or cause the plant to revert to the vegetative state. However, the total amount of light energy it receives each day is significantly less than what is generally recommended. This reduction in daily light integral (DLI) directly impacts the plant’s overall growth potential.
The Trade-Offs of Restricted Light
Optimum light schedules for autoflowers are typically 18 hours of light and 6 hours of darkness (18/6) or 20 hours of light and 4 hours of darkness (20/4). These schedules maximize the plant’s ability to photosynthesize and generate energy for growth and flower production. Switching to a 12/12 schedule means the plant loses a third of the potential daily light compared to an 18/6 cycle.
This restriction on light energy translates directly into a reduction in the plant’s final size and overall yield. Less light means less energy for building structure, resulting in smaller plants with fewer and less dense bud sites. Growers using 12/12 can expect a noticeably smaller harvest compared to those using a longer light cycle.
The shorter light period also limits the plant’s growth during its brief vegetative stage, leading to a smaller structure to support the flowers. To compensate for the loss of light duration, a grower would need to significantly increase the light intensity. Ultimately, the 12/12 schedule compromises the autoflower’s potential, making it less efficient.
Situations Requiring 12/12
Despite the reduction in yield, specific scenarios exist where a grower might choose the 12/12 schedule for autoflowers. The primary reason is when autoflowers are grown alongside photoperiod strains. Photoperiod plants require 12 hours of uninterrupted darkness to initiate and maintain their flowering cycle.
In this mixed-garden situation, the autoflower must be placed on the 12/12 schedule to accommodate the photoperiod plants. This compromise allows the grower to cultivate both types simultaneously, accepting the reduced autoflower yield for simplified management. Another element is that in extremely hot environments, the 12/12 schedule can be used to run the lights during the cooler nighttime hours, helping to manage high temperatures.