As soon as we identified the sex of our plants, we can start flowering the females indoor, or just wait until they do it naturally outdoor
Bloom in cannabis is a gradual process, that usually starts with STRETCHING, which is how growers call a rapid, vertical growth of the canopy, induced by shortening of the photoperiod, except autoflowering varieties, which start blooming when they reach sexual maturity.
Stretching is a big problem for inexperienced indoor growers, who are rarely prepared for how fast and vigorous cannabis can become after it entered flowering. Most of the varieties will double, some will triple in height, and very few will stay low, adding only a couple of inches.
For this reason it's recommended to induce flowering indoor at not more than half vertical space, so when they finish stretching, they don't touch the lamps.
Outdoor it's a fair game. They can grow as tall as you let them, providing you're not limited by any conditions of practical or legal nature.
Duration of stretching is strain dependant, but you have to be prepared for at least 2-3 weeks of it with most of the hybrids. However, pure sativas can stretch for as long as 8-9 weeks, which is something to keep in mind.
While cannabis is stretching, the process is accompanied by flower formation, which starts at the top nodes. In just a few days they becomes calyxes, which then start growing white stigmas, commonly addressed by growers as pistils, pistols or just hairs.
These are nothing else than female reproductive organs, that seek to be pollinated by the males... but growers never let them, and instead keep them virgin, so flowers can eventually become gorgeous buds!
In terms of nutrients, cannabis will use a lot of nitrogen, calcium and magnesium during early bloom with a bit of phosphorus, that's used exclusively to trigger flowering and expand root system in the same time.
However, feeding the plants copious amounts of phosphorus in this stage is a HUGE misunderstanding. Cannabis cannot use more than it needs, and it needs very little of it unless the growth medium or native soil is absolutely depleted.
In best case, plants should be given a bit of it in one or two consecutive feedings after they finished stretching and started producing trichomes to optimise metabolism, particularly sugar production.
Much more important at this point is stepping up watering regimen! We should make sure our plants have always access to it, so they can transport nutrients from the soil and inside their tissue without any effort!
In the same time we ought to start bringing down the RH, regulating the temperature, and inspecting for bugs, always checking the bottom of the plant first, so we can prevent BIG PROBLEMS later on.
Stay tuned for the next bit, and support 
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