Here is the therory:

You can increase your ratio of female plants by coontrolling the enviroment once the plants have three pairs of true leaves.

Higher nitrogen and lower potassium for the first 2 weeks icreases the number of female plants.

Lower temperatures, and higher humidty increase the number of females.

More moisture in soil, and more blue light for females.

Here is what the topic is about....LIGHT TIMES

Fewer hours of daylight (e.g., 14 hours) make more female plants, while longer days of 18 and more increase males.

And of course STRESS!!!! Less stress increases female traits.

ALL of this is from High Times magazine pg 104 of the June issue.