I've read a lot about using ethylene gas to help make more plants turn out female. Ripening bananas placed under the plants... yeah, it sounds fruity, but they give off natural ethylene gas and some people swear it works.

Then again, there was some "scientist" that claimed he could take a seedling sample and run it through all kinds of crazy stuff to look at the genes and tell if it was gonna be a male or female. So that whole debate on making a plant turn totally male or female beats the hell outta me, maybe if it was destined to be a male it could be switched to growing female with the right stuff/hormones.