Trish is so right. It seems like all the national chains must oder in huge lots two years in advance, and distribute with no consideration of zone or if something will survive. They are cleless !
Dahlias are natives of Mexico, so they love warmth and sun. But not al of Mexico is so hot. That might be the problem. In the Valley o Texas, which is zone 9 or 10, depending on the year
they are loved, but when I worked at a nursery, they were sold as, and treated as, annuals.
Afterthought: I have seen dahlia bulbs @ Ho Depo... if you would like to grow a sacrificial dahlia as an experiment.