TLDR; Problem: Potato plant grows but produces low to no potatoes.
I recently tried growing potatoes in my backyard. My zip code is 27587 which I believe is zone 7a. The visible (leaf/stem) portion of the plant kept growing. Per what I've heard, I tried to "hill" the plant up to about 3-4 leafs. The growing medium was about 40% worm castings and 60% hummus. The hummus was labeled organic, and my worms are fed nearly all organic food. I grew this in a felt grow bag, and it grew past the 15 inch grow bag, so I cut out the bottom of another grow bag, wrapped that 2nd grow bag around the plant and hilled it again up to about 3-4 leafs with the same growing soil. When the plant grew again and wouldn't die, I cut another bag and made extended the bag again. I don't know why they don't make expandable grow bags btw.
The potatoes were organic, but I've had similar results with seed potatoes. I waited until the plant wilted and appeared dead before dumping out the soil from the grow bag to show the usual no potatoes. It probably had the sun over it from about 10am-5 or 6pm and indirect light during other daylight hours, blockage was due to a house, garage and trees around it.
I watered it with rain water periodically, but made sure it was never sopping wet, plus the felt bag let water out from the bottom anyway. I don't think it was over-watered, but then it never told me that. Because it kept growing for about 2.5 to 3 months, I assumed it had at least the minimum amount.
I can say that the soil was more packed at the bottom. I don't know if it said, hey the dirt is too tight, let me not make any potatoes, but I don't know what the plant was thinking. I did everything I heard to do with the Potato, but it still didn't like me.