this is from the dutch passion seed company website.
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.
thats what they have to say. i know there are probably 2-4 more variables that give more females but its in my grow bible and i dont feel like searchin.