I've only been growing them for ~7 years so I'm no expert but here's what I found they like:

Water, food, and sun. They don't complain about lots of mulch either :-)

Take any one away and they slow growth. I also fed mine ash from my chiminea in addition to fruit food and they grew so fast they got out of hand.

Unfortunately, four of the "designer" cultivars I bought were unsatisfactory and I just spent the better part of a week removing them to make room for other things.

After fertilizer and water, heavy,loomy mulch is my third ingredient to growing large bananas. Pile on the shreaded pine mulch around the base. Only an observation but I believe it gives the banana corm and roots room to reach out and grow verses a little hole in natural hard soil. Pine mulch is cheap and breaks down very nicely. Mine thrive in it.

i agree with all comments.. i add alot of compost start of every growing season here..dig in deep,mixing native soil in with it..
i tend to be stingy with fertilizer..but when i give them good
feedings regularly.. they get big ..and im in utah..
2 yrs ago..my ensetes,sabas got over 14ft tall..
this yr..im hoping to get big plants again..
for me..sun,good watering,and heavy on the fertilizer..
mulch i dont do..but the soil is heavy in compost..but i agree with bamatufa..
good luck..and keep us posted...