There are some proven methods. @ReikoX describes one in detail here.
Colloidal silver can be used as well. Much more detail and info available on this site if you search. Silver inhibits an enzyme i believe when applied topically and a female plant produces male flowers. Pollen from those flowers carries only female DNA. When a female is pollinated with that pollen, the babies are all girls
Good luck, and keep us updated on your experiment!
