The answer to whether cannabis grows at night is a definite yes, but the purpose of that growth changes significantly once the lights go out. A plant’s life cycle operates on a 24-hour rhythm, where both the light period and the dark period serve distinct, complementary functions necessary for development. The day is primarily dedicated to collecting and storing energy, while the night is the time the plant uses that stored energy for physical construction and structural expansion.
The Role of Light in Energy Production
The light period is the plant’s food-making phase, powered by a process called photosynthesis. During this time, the plant absorbs light energy through chlorophyll in its leaves. This captured energy is used to convert carbon dioxide from the air and water into simple sugars. These sugars represent the chemical energy storage the plant creates for the activities that follow. The length and intensity of the light cycle directly determine the amount of energy reserves the plant can build up in a single day. This stored energy is crucial, as it provides the fuel for all metabolic processes that occur when the light is absent.
Structural Growth During the Dark Period
Once photosynthesis ceases, the plant switches to respiration, which is the process of breaking down the stored sugars to power metabolism. This energy output phase fuels cell division and cell elongation, which results in measurable gains in height and mass. Growth hormones, specifically auxins, play a significant part in this nocturnal expansion, promoting the extension of cells, particularly in the stem and branches. This process causes the characteristic “stretching” or rapid vertical growth often observed overnight in the vegetative stage. The darkness also facilitates the efficient movement of water and nutrients throughout the plant’s vascular system, transporting resources to the growing tips and developing root structures.
How Night Length Triggers Flowering
The length of the uninterrupted dark period is the environmental signal that determines the plant’s life stage. Cannabis is a “short-day” plant, meaning it initiates flowering when the night becomes long enough. The plant does not actually measure the day length, but rather the duration of continuous darkness. If the dark period exceeds a specific threshold, called the critical night length—typically around 12 hours for most strains—a hormonal cascade is triggered. This signal involves the production and translocation of Florigen, a mobile signaling molecule that travels from the leaves to the shoot tips, signaling the plant to switch its focus from producing leaves and stems (vegetative growth) to producing flowers and buds (reproductive growth). If the dark period is interrupted by even a brief flash of light, the plant’s internal timer is reset, and the flowering signal is never fully sent. This sensitivity to the dark period is why photoperiod-dependent strains must be managed carefully to control their transition to the flowering phase.
Optimizing Dark Cycles in Cultivation
Cultivators manage the plant’s growth stage by manipulating the duration of the light and dark cycles. To keep a plant in the vegetative stage, growers use long light cycles such as 18 hours of light and 6 hours of darkness (18/6) or sometimes 24 hours of continuous light (24/0). To induce flowering, the light schedule is abruptly switched to 12 hours of light and 12 hours of uninterrupted darkness (12/12). This consistent, extended dark period meets the critical night length requirement, signaling the plant to begin bud production. Maintaining absolute darkness during the 12-hour night is essential to prevent stress, as any interruption, even a small light leak during the dark cycle, can confuse the plant’s hormonal signals, potentially leading to a return to vegetative growth or the development of male reproductive organs (hermaphroditism). Ensuring a light-tight environment is a fundamental practice in controlled cultivation settings.