I immagine in the next couple years, this thread will have a definitive answer as our hobby grows and more studies are done.The hormones of the plant still have a lot to teach us.
My take on it is the same as people. When you give a man female hormones, he'll grow tits. When you give a woman male hormones, she turns into my mother-in-law. Too many masculine hormones, and anything can happen.
As the grower, the environment you create will most certainly affect the plants hormones. We know slacking here causes hermaphrodites. Are certain strains or genetics more susceptible to this? I would imagine yes... Do the conditions we provide early in life determine the sex though? I don't think me or science have an answer for that yet.
BUT
as someone who has kept and bred many species of gecko, I can tell you 100% that the temperature the eggs are incubated at WILL determine the sex of many many many lizards.
Take leopard geckos for example:
Incubate their eggs between 86-90 degrees, they will be predominantly male.
Incubate them at 80-84, and they will be predominantly female.
Incubate them right at 85? You get a den full of geckos that are confused about their gender and frequently try to mate with their same sex.
I know Gecko's aren't weed, but food for thought.
Personally, I think it's highly possible to produce some kind of hormone or product that will drastically increase your female to male ratio, but I don't 'know' that.
ISK, I LOVE your experiment. But I HATE that you're using tin foil