If I recall correctly, you should carefully dig the tubers when the ends of the vines start to die; OR, just before your first frost.

If the vines are still alive, and drainage is fine, the roots should be fine. As the plants die down, the potatoes go dormant, they don't get ruined. You want them to go dormant for storage.

You can eat them now if you want to, they are perfectly fine to eat, but you don't HAVE to dig them all up now, you can leave some for a couple more months. Some tubers might get larger than you want if you keep them growing, so they may go past their "peak" that way.

Thanks all!

Surprised no one mentioned the curing phase that helps the sweetpotato convert its starch to sugar! https://www.youtube.com/watch?v=2Q57uKLq_lw

I have tried that drying and they started sprouting. For here, it seems they are better off without that hot drying.

I had a tremendous sweet potato harvest...huge vining and tubers.

Our first harvest was very productive, will dig the late ones soon. I do clean them off before storage (a light scrubbing with water) and leave them in the warm garage to "cure for 2-3 weeks. Then store on racks in a dark cool pantry.