Harvest when the stalks yellow and wither. At least that is how it is normally done.
I plant potatoes in January and February. I'm in the Bay Area.
I have been harvesting for the past couple weeks and 2 plant areas still have green stalks so I will wait for those to wither before I harvest.
I think potatoes are 90 day from sowing to harvest, but I find it takes a little longer. Everything sounds normal with yours. As long as they are green and growing, keep watering. You could stick your hand in and feel for a potato to pull if you are curious as to their development.

I tend to cut off the flowers and let the plant keep going until it withers, as DR says. I notice the potatoes do still gain weight after flowering, if I do this. I used to think about a proper season for planting taters, now I shove them in the ground in any month when i have chunks with sprouting eyes on them. I think they are a 12 month crop here in SoCal, as long as they don't get too hot.

Thank you for your help.
Tim

The flowers on my potatoes have grown a green tomato looking fruit.
Does any one happen to know what these are?
Thank you for your help.
Tim

Tim, according to a blog: "Potato flowers turn into potato berries which have tiny little potato seeds in them. Don't eat them."

Yes, you want to plant those potato berries, and they will also grow into potatoes, except they will be hybrids with 2 parents, instead of clones like the eyes are.

Carla in Sac

But doesn't letting the taters go to flower & seed decrease spud production? Pulled these yesterday, anything the size of a marble or less gets washed and saved for replanting, after sprouting.

{{gwi:537201}}

I only have one plant. Are they still fertile?