I'm growing Nadine potatoes in those large black plastic potato bags (sort
of like heavy-duty, short bin liners).

This is the first time I've ever grown spuds. The soil is now up to the top
of the bags, but there's loads of tall stems and leaves above the soil.
They're just beginning to show flower buds.

Do I simply leave them and dig around when I want the potatoes, or is there
a correct time to harvest?

Thanks.