Hi, let me preface this with not only am I a newbie to this forum, I am a NEWBIE period to growing, so having said that...when I read this post, I recalled reading something in my beloved growers bible indoor/outdoor by cervantes about growing more females. Sure enough, I quickly found it. I would think cervantes knows what he is talking about (I have been greatly impressed by the book) and I believe too, in fact the plants sex is not predetermined at just the presence of a seed (my opinion, based on this book & the knowledge of have accumulated thus far).
The book says, environmental factors start influencing sex the moment the seedling has 3 pairs of true leaves (not counting cotyledons). So this jives with what the old man said. Couldn't find readily, anything about the dark period prior, but really seem to recall reading that as well, as another poster had mentioned cervantes said.
So the influences after the 3 pairs are present, that I will try among those included to increase the odds of a female plant are: lower temps/higher humidity, more nitrogen & less potassium first 2 wks., more blue light, and fewer daylight hours 14 opposed to 18.
This thread just caught my eye, & I thought I would chime in, because usually the old timers REALLY are the ones that know their stuff and every once in awhile if you are lucky, they share some of life's "gems of wisdom".
Anyway, I am just trying to get something going from bag seed right now, for the 2nd time. 1st time around, germed 3, one root was like 2 inches long before I planted it (like grew overnight) the other 2 barely out of shell. Well that long rooted one popped up like nothing, grew like crazy, THEN reailized what stretching was, etc. So what I thought was my SUPER baby boy, was on its way to death stretching itself to a pitful thin nothing trying to reach my weak light that was WAY to far away. Then when I figured it out, I moved it closer (too close for that type light -grow-lux grow light), & burned his ass to death the rest of the way. Other 2 never came out of the soil. TRIED with grow light, just to start since was just testing it out, & have a low starting budget, know now I cannot even use that & will get some cheap CFL's to grow my few little plants this next time.