I've got a couple of drawf banana trees that overwinter in the greenhouse but stay outside during the summer. They seem to be thriving and are now about four to five feet tall and are developing side shoots. Right now I am using osmocote, but next year will switch over to a more natural concoction including compost, and a mix of cotton meal, blood meal, bone meal, kelp meal, lime and ironite. Banana trees like to stay constantly moist but not heavily wet. So make sure your soil has plenty of perlite or similar component for good drainage. Be sure to read up about how and when to cut back the main trunk after fruit production. I recently got first hand instruction on that from a local in Belize.