Ok at 18" it will with good light it will be 36" when done flowering but I cannot stress how badly you need more lights at least get one 125w flourecent from ebay or hydro shop make sure you get 2700k or (kelvins) red spectrum this is the spectrum needed for flowering beacuse i used full spectrum and what i got from it was not worth all my effort. No one little light just won't do it if the 45watts are all you can afford try to get as many as you can on it! Sex is easy if it gets balls its a boy if little white hairs it's a girl should start showing around 2nd or 3rd week into flowering. -goddluck