If you are looking for fall color in a hot site then Rudbeckia, Echinacea and Sedum 'Autumn Joy' are heat loving perennials that won't wilt in the afternoon heat. Mums and dwarf dahlias will also add late summer and fall color. Don't forget to add some tall and wispy texture in the back of the container with ornamental grasses such as the Pennisetum, Carex grass and Festuca grass. Sounds like you will have fall fireworks in those pots. Keep growing, Marianne Binetti