Indoor growers wanting to know how to flower cannabis will find the process to be very easy and quite interesting. Once you have grown your plants to the desired height, you end their vegetative growth stage and begin their second stage of development called the “flowering” or “budding” stage. This is where both male and female plants are switched into reproductive mode. Structures on the plants called calyxes that are grown for pollination by male plants are intentionally kept from being pollinated by the removal of any male plants from the grow closet. When the female plants aren’t pollinated, instead of producing seeds they produce buds, or colas, laden with THC.
In order to force this change, there are essentially 3 things you’ll need to do:
1) Switch them from fluorescent light to a high pressure sodium (HPS) grow light that provides both the power (in “lumens”) and the shorter red-shifted light frequencies that cannabis plants need during the flowering stage. Make sure you buy the brightest grow bulb you can afford. This will help maximize the overall yield and quality of your plants. Most hydroponic stores carry them.
2) Put your plants on a strict (preferably timer-driven) 12-hour lights on, 12-hour lights off schedule. This will trigger the hormonal changes in the plants that force them into reproductive mode. It’s also important to preventing any light seepage into your flowering area during the lights-off periods. Exposure to even the faintest ambient light in the area will confuse your plants and slow down calyx / bud development. Try to water and take care of your plants only during the lights-on periods.
3) It’s time to convert your plants to a more phosphorous and potassium-rich mixture of nutes that they’ll need for bud growth and THC development. Many growers continue to give their plants nitrogen during the flowering stage, but in decreasing amounts at the same time they’re increasing the phosphorous and potassium ratios. All nitrogen feeding should completely stop 2 or 3 weeks prior to harvest.
After a couple of weeks into the flowering stage, you’ll start seeing the formation of the delicate white-hairy buds (calyxes) up against the main stem and on the ends of some branches. Unfortunately, you may also notice that some of your plants are male in gender, and which need to be promptly dealt with.
Sexing Your Plants
Only the female cannabis plants produce appreciable amounts of THC; the male plant’s THC concentration is very weak and relatively useless. The male’s primary role is to propagate the species. Unless intending otherwise, male plants need to be removed just as soon as they identify themselves as male. Males start revealing their gender about two weeks into their flowering period. If you don’t remove them in time:
- the males’ pollen sacs will mature, break open, and distribute their wind-borne pollen.
- the female plants will capture that pollen with their hairy little stigma and the calyxes will become fertilized.
- now fertilized, the female plant will concentrate the majority of her remaining time and energy producing seeds instead of THC.
So, unless you’re planning on creating your own seeds for later use, remove any male plants as soon as they’ve exhibited themselves as male.