High THC Content and Bud Density

Cannabis Reproductive or Flowering Phase

The sex is clearly revealed. Males produce little balls clustered together like grapes. Most plants (except autoflowering strains which flower independently of photoperiod) will flower under diminished light. In nature, cannabis plants sense the forthcoming winter as the earth turns and daylight reduces in duration. If females are not pollinated, they will start to produce buds containing sticky white resin glands or trichomes in a final attempt to attract male pollen. The trichomes contain the largest amounts of THC and CBD, the two main psychoactive substances. Indoors, flowering is induced by keeping the plant in complete dark for 12 hours every day, until it is ready to be harvested. If manipulated, a female can either generate a seedless bud, a bud with a few seeds, or a bud that is almost totally seeds. The first case is achieved by removing all the male plants before any of their flowers open, the second occurs when one or more male flowers have barely burst open and then removed and the third case occurs if the males are let to fully pollinate the females.

Buds of the first case are called sinsemilla (it is really two words: "sin semilla," which translates to "without seeds" in Spanish, but is often misspelled as one word). The resultant cannabis contains the most Cannabinoids possible. The amount of Cannabinoids in sinsemilla is considerably more in comparison to cannabis that has been grown in a pollinated environment, because the production of seeds requires an immense amount of energy, and if left unpollinated a female plant will divert all her energy to calyx production in an effort to seize pollen. This is especially desirable, as the calyx is where the highest concentration of trichomes exists, and the more densely packed a plant is with calyces, the greater psychoactive effect that plant will likely have. Potent sinsemilla is especially important to medical users, to minimize the amount of cannabis they must consume in order to be afforded relief. Cannabis with seeds is generally considered to be of inferior quality and/or grown with inferior technique. Common terms for seeded, or otherwise low-quality, cannabis are "mids," schwag, "regs," "booty," or "mersh".

Indoors, plants like cannabis are induced into flowering by decreasing its photoperiod to at least 10 hours of darkness per day. Traditionally most growers change their plants lighting cycle to 12 hours on and 12 hours off. This change in photoperiod mimics the plant's natural outdoor cycle; with up to 18 hours of light per day in the summer and down to less than 12 hours of light come fall and winter.

While the flowering hormone in most plants, including cannabis, is present during all phases of growth, it is inhibited by exposure to light. To induce flowering, the plant must be subject to at least 8 hours of darkness per day; this number is very strain-specific and most growers flower with 12 hours of darkness to be safe. The flowering hormone is very quickly inhibited, taking less than two minutes of exposure.

Flowering usually lasts from 45 to 90 days indoors. If growing outdoors it may take somewhat longer, depending on the natural onset of the colder seasons. The flowering length is mainly genetically determined with plants as pure cannabis "indica" strains flower in as low as 45 days, while plants as cannabis "sativa" can take up to 4 months to finish and the harvest yields significantly less. This is also the main reason why certain plants, like cannabis indica, are almost always grown indoors unlike cannabis sativa, which is also grown outdoors.

Some cannabis members of the subspecies Ruderalis, will begin the flowering cycle without a significant reduction in their photoperiod.

Flowers from certain plants, like cannabis, are called "calyx", and are with cannabis the most prized part of the plant. In late flowering the calyx are easily visible to the naked eye. Calyx development begins approximately 1–2 weeks after the photoperiod is reduced. In the first weeks of flowering a plant usually doubles in size and can triple. Calyx development ends around 5 weeks into flowering and is proceeded by a period of calyx “swelling”. During this time the buds greatly increase in weight and size.