I'm still a newby with 3 grows behind me but here is some info I have found helpful.

Question -- If I have to pay large money for seeds how can I increase the percentage of seeds that produce female plants (I pull the males as soon as I can tell the difference)?

Answer -- These are from the Castaneda Bible and have worked well for me:

*Temperature - females like lower temps.
*Humidity - females like higher humidity
*Moisture - females like more water
*Light - females prefer more blue-spectrum light
- females like fewer hours of light while germing
*Nutes - females like increased nitrogen
" " decreased potassium

I germinate my seeds in total darkness inside a baggie. I open the baggie every day and exhale a lungful of CO2 before sealing the bag. Last batch was 10 females and one hermie/male.

Good Luck, BigSteve.

well.... there are some things to consider here. there is a big debate as to whether seeds sex is predetermined, which i think is probably the case. i've almost always had good female ratios, but then again, i use mostly my seed stock. if these things hold true, i'd like to agree with which parts.....

cool temps = more females
blue spec = more females
high nitrogen = more females

warm temps = more males
warm spec = more males
high phosphorous (potassium matters not) = more males

hope this helps! do NOT follow dutch passion's advice on increased females.

wow, awesome post...

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I've heard low pH (<6.0) in soil media will push plants to be male.. but that's just hearsay. I haven't experienced it.

at what point do you think sex is determined then?

I followed most of that advise during germ / seedling but things got a little warmer during veg.

Is it better to CFL during veg then (more Blues, less heat)?
I have a hps, would it be better to save it until flowering?

that depends; if you want to veg 30 plants quickly, go hps. if you want to veg one plant slowly, use cfl's.

cfl's suk for growing applications

my understanding is that the sex is determined in the 2 weeks time that the seed sprouts until the vegetative stage. Once the plant goes from seedling (mostly root growth) to vegetative (plant growth), the sex has been determined. When the plant grows its 2nd or 3rd set of leaves, clone it and flower the clone. There is no sense in wasting time and taking the risk vegging out a male, am I right?

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- Pink Floyd

The plants sex is predetermined in the embyro of the seed. You cannot make more females by doing the things you meantioned, they are mearly guidelines to follow to treat the female with the best care...the plant will be, what the plant will be.

The only thing you can do to a plant is make a female turn hermie by stressing the fuck outa it.

i also lean to this side of the argument. as stated before, if any conditions play a part, they are the three i listed.

i have not been able to prove that seeds are predetermined though; i've done many tests of seeds from shape and size, none of which were flawless examples. i do not think that plants decide if they want to be female or not.

no, that actually takes longer. if you chop the top, you stress both parts, and both will show gender later. the best way to find sex is to veg until preflower, and clone your best girls.

as for sex being determined at 2 weeks in, that fits in the debate. the big question is if sex is predetermined or not, and the truth is no one really knows for sure.