Carolyn:  Thank you so much for your reply.  Very encouraging to learn one can grow tropical fruit in zone 6.   I am planning on building small greenhouse- about 12x25 ft in size, but was not contemplating that I would go to the expense of heating it in winter.  I plan on keeping my potted plants in about 10-gal pots for a while so they can be moved easily inside a walk-in basement.  When they have to go into bigger containers I might eventually look into building some kind of solar heat-capturing contraption for the greenhouse. I have some questions about the "behavior" of these plants during the cold months if the temp gets down to 40-50 degrees.  My interest right now is in figs, guavas, dwarf pomegranates, dwarf papayas, star fruit, and possibly dwarf mangoes. Would they drop their leaves and go dormant during winter.  I am wondering if these plants drop all their leaves, but would otherwise survive, if kept in a dimly lit walk-in basement that stays at around 50-55 degrees during the winter.  Thanks for sharing any insights.    Regarding the expense of huge pots, I have found a cheaper solution:  I can get 60-gal food grade plastic barrels at $10 each.  They have two small holes at the top with screw in caps.  I cut the barrels across the middle and drill holes for drainage.  That gives me two large, 30-gal pots, at $5 each.    Their only "drawback" is they are blue in color. 

New to this forum and also a novice in trying to grow tropical fruit in containers in NJ, zone 6b.   I am looking for some not-too-expensive source for getting some dwarf papaya and dwarf star fruit plants for growing in containers.    Thanks for any ideas and tips.