The cannabis flowering stage is the plant’s reproductive phase, where it develops the resinous flowers, or buds. This transition from vegetative growth to bloom is a response to environmental cues, most commonly a reduction in daily light hours. The duration of this period is highly variable, generally ranging from six to fourteen weeks. The timeline is heavily influenced by the plant’s genetic makeup and environmental conditions.
How Plant Genetics Set the Timeline
The primary factor determining the flowering duration is the plant’s genetics: Indica-dominant, Sativa-dominant, or autoflowering varieties. These lineages evolved in different geographical locations, leading to distinct maturation schedules. Indica-dominant strains, originating in harsh, mountainous regions, typically have the shortest flowering periods. They mature in approximately seven to nine weeks indoors, an adaptation allowing them to complete reproduction before cold weather arrives.
Sativa-dominant strains hail from equatorial regions with long, consistent summers, resulting in a much longer flowering time. These varieties often take between ten and fourteen weeks, or longer, to fully mature. Their growth pattern reflects this, as they continue to stretch vertically well into the flowering phase.
Autoflowering varieties operate on a different internal clock, as their flowering is not dependent on the photoperiod or light cycle. They contain Cannabis ruderalis genetics, causing them to transition automatically after three to five weeks of germination. While their total life cycle from seed to harvest is short (often eight to twelve weeks), their flowering stage is integrated into a rapid overall maturation.
Distinct Phases of the Flowering Cycle
The flowering stage unfolds in distinct, predictable phases regardless of the total duration. The first phase, called the pre-flower or stretch, spans approximately the first three weeks after the light cycle change. The plant experiences a rapid vertical growth spurt to support the developing flowers. Small, white pistils begin to emerge at the nodes, signaling the start of flower development.
The bulk or mid-flower phase generally occurs between weeks four and six. Vertical growth slows considerably as the plant focuses energy on developing flower structures. Buds visibly swell and pack on mass, and resin production becomes noticeable. Energy demands are higher during this phase, requiring increased levels of nutrients like phosphorus and potassium.
The final phase is the ripening or finishing stage, taking place from week seven onward until harvest. Buds stop increasing in size but focus on increasing density and potency, becoming hard and sticky. Chemical changes occur as the plant converts cannabinoids and terpenes, signaling final maturity.
Environmental Factors That Affect Duration
While genetics set the blueprint, external environmental factors significantly influence the actual flowering duration. For photoperiod strains, maintaining a strict 12 hours of uninterrupted darkness is necessary. Light cycle consistency is paramount because brief exposure to light during darkness can interrupt hormone production, potentially delaying or reversing the bloom cycle.
Temperature and humidity extremes slow down metabolic processes, extending the time needed for flowers to mature. If temperatures are too high or too low, the plant becomes stressed, interfering with nutrient uptake and energy conversion. Optimal temperature and humidity ranges allow the plant to progress at its genetically determined pace.
Improper nutrient management can halt development, causing delays as the plant struggles to recover. Both deficiencies and “nutrient burn” from overfeeding stress the plant, forcing it to expend energy on self-repair instead of flower growth. Providing the correct balance of nutrients, particularly higher phosphorus and potassium, is crucial for maintaining momentum.
Determining the Exact Time to Harvest
The ultimate measure of the flowering stage’s duration is determined by visual indicators that signal peak maturity. One of the first indicators is the appearance of the pistils, the white, hair-like structures emerging from the buds. As the plant matures, these pistils darken, curl inward, and change color from white to red, orange, or brown. Most growers aim to harvest when 50% to 70% of the pistils have changed color.
The most precise method involves microscopic examination of the trichomes, the tiny, mushroom-shaped resin glands that coat the flowers. The color of the trichome heads indicates the maturity level and chemical profile of the cannabinoids within. Trichomes start clear and translucent, indicating an immature flower with low potency.
Trichomes transition to a cloudy or milky white color, signifying the period of peak THC concentration. Finally, they turn amber, suggesting that THC is degrading into compounds like Cannabinol (CBN), which leads to a more sedative effect. The final harvest decision is a balance, with most cultivators cutting plants when the trichome ratio is mostly cloudy with a small percentage of amber.