Alice_ma6,

1) The bigger the better at least a gallon + - to make room for a good root system and also for tuber development. Some can get really large.

2) As many holes as possible. I take pails and drill holes in the sides near the bottom to plant my brugmansia. That way I can root prune easily and pull them out. Dahlia roots are not as large as brugmansia, so bottom holes will be okay. You still might have to dig deeply to get to the bottom of the pot.

3) Good soil with lots of nutrients. Also with good drainage. They don't like wet feet.

4) If your pot soil is good, you will need less fertilizer. I use Miracle Grow, but any balanced fertilizer is good.

Personally, I don't have the space to do what you are recommending, so I clean well, dry slightly, dust with bulb dust, wrap, and store in cardboard box in my cold cellar which does not freeze. This has worked well for years.