If you will run your light vertically, with your size pots and good care, that 600 watt will easily get you your one pound from 3 trees.
It will take a complete two months Veg to do it, but it can easily be done.
If you will let the Trees you have on this grow, go until their completely done " full amber, " you will be surprised how much those girls will still fill out on this grow.
Running the bulb vertically " even hanging naked without any protection is fine as long as nothing is right on it or you spray water while it is hot.......common sense applies, " however you will get an explosion of growth on the sides of those girls in the last few weeks, by doing this in this grow itself,,,,trust me my friend.
Good luck and remember " seven gallon pots, good care and that 600 vertical will easily give you your goal. "
Blessings,
Rev. TheNatural