Look what I found for you...

Page 261 of the bible.

"Enviromental factors star influencing se the moment the seedling has 3 pairs of true leaves. Factor include but are not limited to:

-N and K levels. Increasing N makes more females. Lower N makes more males.Increase K increases the tendency for males;Lowering K level encourges female plants. A higher N level and lower K level in the first two weeks increases females.

-Temperature: Low temp increase the number of female plants. Warm temp makes more males.[I know this first hand having turned 9 plants into males]

-Humidity: High humidity iincreases the number of female plants. Low humidity increases male plants.

-Light Spectrum: More blue light incereases the number of female plants[MH]. More red light increases male tendencies[HPS].

-Photoperiod: Fewer hours of daylight(e.g. 14 hours) increases the number of females. Longer days (e.g. 18 hours) make roe male plants.[think of all those people on 24 days]

Stress: any enviromental stress tends to yeild more male plants when growing from seeds."