Nothing of that nature will survive the whole summer in full sun. They just get too hot. Snaps will die off by the end of June, but will reseed. Sunflowers will grow and the branching varieties will keep blooming well into July, but again, they aren't meant to last all summer, either.

If you want something that will take the heat and sun, try Gazania. They do need frequent, liberal waterings, but they will be okay and hang on through the summer. Although they'll probably look a bit ratty by August, they'll sometimes reseed and come back on their own.

You might also try some ruellia or cape honeysuckle. They're bushy, but will tolerate quite a bit of heat as long as they get water every so often.

lisianthus and vinca.

canna and datura.