Many researchers have suggested that sex in Cannabis is determined or strongly influenced by environmental factors.
Schaffner, J. H. 1931. The fluctuation curve of sex reversal in staminate hemp plants induced by photoperiodicity. American Journal of Botany 18(6): 424-430.
Ainsworth reviews that treatment with auxin and ethylene have feminizing effects, and that treatment with cytokinins and gibberellins have masculinizing effects.
Ainsworth, C. 2000. Boys and girls come out to play: the molecular biology of dioecious plants. Annals of Botany 86(2): 211-221. Retrieved on 24 February 2007 hxxp://aob.oxfordjournals.org/cgi/reprint/86/2/211
Environmental cues such as fooding, drought, chilling, wounding, and pathogen attack can induce ethylene formation in plants. In flooding, roots suffer from lack of oxygen, or anoxia, which leads to the synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC). ACC is transported upwards in the plant and then oxidized in leaves. The ethylene produced causes nastic movements of the leaves.
Spinach plants raised under water restriction displayed a male-biased sex ratio while plants raised under sufficient water conditions displayeda more even or female-biased sex ratio
hxxp://www.academia.edu/1789755/Biased_Sex_Ratios_in_Plants_Theory_and_Trends
so in conclusion under watering can lead to more males in dioecious plants
another factor is ethylene production will lead to more females making supper cropping an excellent way to get a female plant.