They shouldn't fall over, shouldn't need any fertilizer.

Lots of sun, water and you can feed them with 20/20 every so often. Height depends on the variety. They are sturdy upright plants and don't require any staking.

If you want to fertilize, I suggest Milorganite. It is a pretty gentle (but stinky) fertilizer. And it is also used as a deer deterrent; can't say 100 percent sure on whether that works or not. Bulbs like Canna seem to love it. I have a canna that blooms yellow flowers. It isn't in the greatest area but has doubled in size and is full of blooms.