Dahlias need lots of sunlight, preferably six to eight hours per day. They can handle a bit of shade, but dahlias really prefer a sunny location. In most locations, the more sun your dahlias receive, the more they will bloom. However, in hot climates in the South, or very dry climates, dahlias can be beaten down by too much heat. If you live in Zone 8 or 9, place your dahlias in a location where they receive afternoon shade, to protect them from the hottest part of the day.