Ideal temperature for bananas is probably around 80-85 degrees (daytime) with at least 60-75% humidity. You don't say where you live or if you have any concerns about the expense of heating a greenhouse that high thru the winter. Absolute minimum temps I'd guess would be around 40-45 (nighttime), although at those temps plants will slow way down. The warmer you can keep the greenhouse at day and night, the faster your growth will be, and more likely you can get bananas to ripen. At colder temps bananas may choke and the main stem may die, but many pups will survive.

You can probably go to different web sites to see how tall the many, many varieties of bananas grow.

Keep us posted on your progress!

thanks dave,
i live in south-eastern australia and we're just coming out of winter now. the nights have been about 23-35F and the days up to 68. Summer is about 95.
do you have any recommendations on the sort of heating i should use and how much it would cost?
thanks!

Vegegrower,

Wow! Australia. OK, well, I couldn't even guess what your utilities might be like. I get by with a small electric heater to heat my garage enough to keep it above freezing. You're fairly mild, so I would think you might get by with electric, but what to do if the electricity goes out? Do you have a generator? How large a greenhouse are you thinking of? If large, you may want to go with natural gas, if that is a option for you.

we're on mains electricity - natural gas MIGHT be an option, not quite sure. i'll look into it.
for size i was thinking maybe about 3.5m by 2m(?) (perhaps bigger we will have to check the budget) and 2.5m high tops.