The cannabis life cycle culminates in the flowering stage, the reproductive phase where the plant shifts energy from growing stalks and leaves to producing flowers, often called buds. This transition from vegetative growth marks the point where the plant develops cannabinoid-rich structures. The timing of this shift is the most important factor a cultivator controls, directly influencing the final yield size and harvest quality. Understanding how this stage is initiated is fundamental to successful cultivation.
The Critical Role of Light Cycles
For most cannabis varieties, flowering depends entirely on a biological response to uninterrupted darkness. This phenomenon, known as photoperiodism, means the plant perceives the change in season through the lengthening of the night. Cannabis initiates flowering when the period of darkness exceeds a specific threshold, mimicking the natural progression from summer to autumn.
In an indoor environment, growers trigger this transition by manually changing the light schedule, typically from 18 hours light/6 hours dark to 12 hours light/12 hours of complete darkness. The plant measures the duration of continuous darkness. If this dark period is interrupted, even briefly, the plant can revert to its vegetative state or fail to flower effectively.
This process is mediated by photoreceptor proteins called phytochromes. During the long night, the active form of phytochrome reverts to its inactive state, signaling that the days are shortening. This signal leads to the production of florigen, which travels from the leaves to the growing tips. Florigen instructs the plant to develop reproductive structures. The switch to 12 hours of darkness provides the continuous night required for the plant to begin its reproductive phase.
Understanding Autoflowering Varieties
Autoflowering varieties are a significant exception to photoperiodism, possessing genetics derived from Cannabis ruderalis. These plants evolved to flower based on their age rather than relying on external light cues. This adaptation ensures the plant reproduces quickly before harsh environmental conditions set in.
Autoflowering plants typically begin flowering automatically within two to four weeks after germination, regardless of the light schedule. They do not require 12 hours of uninterrupted darkness and will flower even under continuous light. Their life cycle is genetically predetermined, meaning the switch to flowering is internal, not an environmental response. This independence allows for a faster cultivation period and greater flexibility.
Identifying the Start of Flowering
Once flowering is triggered—by light cycle change or genetic age—the plant enters the pre-flowering stage, providing the first visual confirmation of the transition. This stage is identifiable by small structures, known as pre-flowers, appearing at the nodes where leaves and branches meet the main stem. These structures are the plant’s rudimentary reproductive organs.
On a female plant, the pre-flower looks like a small, teardrop-shaped calyx, from which one or two tiny white hairs, or pistils, emerge. The presence of these pistils confirms the plant’s sex and entry into the reproductive phase. Conversely, a male plant forms small, round, ball-like sacs at the nodes. These pollen sacs must be removed immediately to prevent the pollination of female plants.
The Timeline of the Flowering Phase
Flowering initiation is only the start of a multi-week process, as the subsequent duration is largely dictated by the plant’s genetics. The full flowering phase, from pre-flowers to harvest readiness, generally lasts between 8 and 12 weeks for photoperiod strains. This timeline varies significantly depending on the plant’s dominant lineage.
Genetic Timelines
Cannabis indica-dominant varieties typically have a shorter flowering period, often finishing in 8 to 10 weeks. In contrast, Cannabis sativa-dominant strains require a longer maturation time, extending the flowering phase to 10 to 14 weeks. Environmental conditions also influence development speed; precise control over temperature and nutrients helps optimize the plant’s progress. During this phase, the plant focuses on developing and maturing the flowers, slowing its upward growth after an initial stretch.