Heres a quote from dutch passion seed company that says:
From literature and our own findings it appears that the growth of a male or female plant from seed, except for the predisposition in the gender chromosomes, also depends on various environmental factors. The environmental factors that influence gender are:
* a higher nitrogen concentration will give more females.
* a higher potassium concentration will give more males.
* a higher humidity will give more females.
* a lower temperature will give more females.
* more blue light will give more females.
* Fewer hours of light will give more females.
It is important to start these changes at the three-pairs-of-leaves stage and continue for two or three weeks, before reverting to standard conditions.
