Hey there michealpeg,

You are correct that a plant does not need 12 hrs of dark to flower, but most hybreds we grow will need more then 8 hrs of dark period to induce flowering. Typically 10 hrs or more of darkness is needed. Also the amount of dark time needed to induce flowering is more then the amount of dark time needed to keep it in flower.

12/12 has become the de-facto standard for indoor growers because it works with at least 95% of what is being grown. It will not work for landrace sativa's or very heavy dominate sativas. They will continue to veg till they are ready to flower, determined by something else.

When a plant is growing, every time it goes dark it starts to make certian chemicals (auxins) and a hormone (floragen) and when it sees light these chemicals break back down. It takes a certian level of these, for multiple cycles, before the plant is induced to flower. This level is strain dependent.

Hope this helps in understanding flowering.
BTW, the flowering stage of all plants is the least understood stage by plant biologists. It is only in the last 10 or so years that the hormone related to flowering was idenified and it appears that many auxins are hormones. Also textbooks written before 1990's typically say that a plant once into the developement stage of flowering cannot be put back into a vegative state but we have learned since, that just ain't so.

OM :jointsmile: