I've always considered dahlias a perennial. Family Compositae. Sunset Western Garden Book describes them as 'perennials grown from tuberous roots.' Since I don't have to lift them, I treat them like any other perennial I grow - plant it, fertilize it, enjoy it, mark it in the fall, look for it in the spring. Most make it, some don't. The same is true for my other perennials. The issue dahlias have in my climate is their roots rotting from too much moisture over winter rather than freezing temps. Some folks do lift them, and I helped my neighbor dig, label, and store a huge amount one year. That was a bit daunting. I then spoke with Dahlia-Dave, a local officianado, and he advised digging/storing a few roots from those I really liked (or were more expensive) to have as a back-up if the in-ground roots failed to return. I don't even do that now. If I can get them past the slugs as they are emerging, they are good to go.
