You're so lucky to have a system like that. Before my a/c went out I planted some cannas and elephant ears where it would drain and I'd never have to water them. My Dwarf Namwah,(the smaller one in the front) I've had for 2 years now. It took my Orinoco a while before it produced large leaves and the pseudostem is almost 6 ft tall. The dwarf namwah pseudostem is a little over 4 ft tall now. What type of fertilizer do you use on your bananas?
