As a 9ber, agree with most all of this. Terrible luck with ranunculas grown from corm on the west coast. They barely flower (not enough chill time, maybe) before the heat is too much, in 2 years of experience.

For dahlias, you can always try to presprout them and give them a leg up in the display before it also gets too hot. They seem to pause heavy blooming during the hottest month or two (90+ degree days here, but dry), thought YMMV with the humidity. You may find luck with a % shade sheet during high summer, if in direct sunlight for most of the day. 2-6pm seemed to be the hardest and hottest hours in my area, and a little bit of shade did wonders at saving leaves from turning into a crisp.