What kind of flowers can I use on the balcony?

anything you want that would do well in your area. just would probably do low plants.

For tall planters, depends on what type of sunlight you get, use potato ivy plants, petunia wave hybrid or geraniums , lobelias and of course tall ferns( put in very center of planter). Be creative in regards to color selections!

Well every year I've been buying a large planter (plastic) say 36" long from a store It has a variety of flowers and it survive well on my balcony I put it on my Garage sale wicker Vanity table holds it quite well and I paid $25.oo for by the time you buy a lot of plants or hanging baskets this is cheaper in the long run enjoy your garden wherever it is

Geraniums are good in that they can handle a tough heat area like a balcony. I also like adding creeping jenny that spills over the pot and trails. If you don't like geraniums, zinnia and cosmos are great flowering plants..

Have you considered this type planter for over your railing with trailing plants for extra color? There are many different styles that hang on the railing. for your existing planters I would put something tall(ish) in the center, with lower growing plants around the edge. For successful plants buy according to sun tolerance.