The flowering stage is the one that all cultivators eagerly look forward to. It is the time when cannabis plants put all their effort into growing large, lush resin-covered buds.
In nature, this stage takes place at the end of summer/early autumn (with the exception of the autoflowering Ruderalis) when decreasing  daylight signals to the cannabis plants that their lives are coming to an end. In response they trigger their reproduction cycles to ensure the survival of the species.
During the flowering period of your cannabis plants' lives, the females start developing buds in order to receive pollen from male plants ( to create seeds). You need to make sure you prevent this from happening, (unless you want seeds all over the marijuana), by moving the males to another area. This will cause the females to grow even larger buds as they strive to attract pollen.
You will also notice during this stage that your plants  exhibit a lot of branch and leaf growth causing your cannabis to become more Christmas tree shaped. This is for two reasons: firstly to support more potential flowers and secondly to increase leaf surface area so that the plants can obtain as much light as possible le – gaining as much energy as possible to focus on bud growth.
Growing indoors gives you a lot of control over this stage as it is a completely artificial setting. When you are ready for your marijuana to enter the flowering stage you can change your photoperiod to simulate the change of seasons. Say for example,  you are running your grow room on a 18/6 photoperiod; by changing to 12/12 you are effectively telling your plant that it is time to start thinking about reproduction.

As mentioned, during the flowering stage of your cannabis plants' life cycle you should be exposing them to 12 hours of light followed by 12 hours of darkness. This is the required light cycle to induce and maintain flowering.
Ideally you need to use an HID light with a bulb that falls into the orange/red colour band. This is the colour band that can help promote healthy flowering, (see our article on colour bands for more info). Using an HID light will ensure that the cannabis is getting the right quality and amount of light it needs.

During the flowering stage the requirements of your cannabis will shift from nitrogen, to potassium and phosphorus emphasis. Much like the other stages, your cannabis still requires all three, but the production of buds requires the plant to use more potassium and phosphorous. 

Flowering Stage