In my experience, digging too early results in tubers with an 'off' taste.
You can pull a plant and determine for yourself... I pulled one last week, it had tubers...
I really doubt that you are going to see much in that pot...
I've never seen shux for tubers when I attempted pot culture...
I used to grow these in wet clay... Like where you find apios vines growing naturally. They grew extremely well for me there...
I'm in dry sand now, and they grow, but don't produce well.
As far as harvest?
My experience is to wait for frost... and only dig what I'm going to eat that day. Sun chokes do not store well... better to leave them in the ground through the winter, digging as needed.
