Hardy Banana's

I bought 2 Banana trees 3 years ago. They grow and put out nice leaves, but they do not get very tall. Driving home the back way yesterday I noticed a house that has a hedge of them almost 15 feet tall. Is it because she separates all her pups from the main trunk, it gets more full sun all day, it gets more water, or she gives them fertilizer? What do you think?
I have separated the pups from the main before and gave my neighbor 2 nice ones. But this year I left some pups attached.

" Is it because she separates all her pups from the main trunk, it gets more full sun all day, it gets more water, or she gives them fertilizer?"

All of the above, but it could also be because it's a taller growing variety. They are gross feeders and thrive on lots of fertiliser and water.

What kind of fertilizer do they like.?

Something like Blood&Bone, and plenty of compost. Commercially they're usually only allowed 3 stems per stool, one small sucker, one mid sized and one full sized flowering. That concentrates the nutrients into the coming fruit with a replacement ready in place when the older stem dies. If they're uncontrolled they produce too many half starved stems.

Ok, I had planed on digging up that bed this fall and adding more compost to it.
I know the soil is not that good. Mine are the no fruit kind, just foliage.
Next year I will get a good food for them and remove all the babies and give them away.

Sounds like a good plan. Since they're only ornamental any good nitrogen fertiliser should be okay.