Cannabis is considered a short-day plant that flowers in the fall. It regulates its growth and flowering stages by measuring the hours of uninterrupted darkness to determine when to flower.
Flowering Week by Week
Within three or four days of initiation to a daily dark period of 10-11 hours, cannabis changes its growth pattern from vegetative to flowering. After that it is on a course that ends with bud ripening. Most modern plants take 7-9 weeks, although some sativa strains take longer.
Week 1: The plant slows down its growth
Week 2: The first flowers appear at the nodes
Week 3: Vegetative growth continues as the plant grows a total of between 25-50% larger than when flowering started.
Week 4: Vegetative growth has ended and the plants concentrate more of their energy into flowering. Odor becomes more noticeable as the plants start to produce capitate trichomes.
Week 5: Flower growth proliferates quickly. The flowers become thicker in areas where they have previously grown and they appear in new places along the top of the branch. The odor increases as more trichomes are noticeable and the odor intensifies a little.
Week 6: Flower growth continues in varieties that take longer to mature. It slows and then stops in seven-week varieties as the plants begin to ripen. The calyx behind the stigmas begins to swell. The odors of the seven-week varieties intensify.
Week 7: The calyxes in the seven-week varieties swell to near bursting as THC is produced in the glands. At the end of the week they will be ready. The trichomes stand more erect and the caps swell with newly produced resin. At the end of the week the flowers reach the peak zone. The odor is intense and the glands, filled with resin, fluoresce. Growth stops in the eight-week varieties as the flowers start to mature.
Week 8: The flowers are ripe by the end of the week, and reach the peak zone in the last 72 hours. After that, they will start to deteriorate if they aren’t harvested.