Ok, several things:

Seed tubers should be planted before last frost, about a month before. So you planted late, and too deep. About two inches deep is good. It will be a little while yet before you see foliage. The tiny new potato was produced entirely by the energy stored in the seed tuber. This can and does happen without sunlight, or any light. It happens every year in my root-cellar, sometimes even take a little harvest of new potatoes out of the root-cellar.

Anyway, it is another indication that you planted late, with overly-sprouted seed.

You can plant them kind of deep, but only cover them up about 1 or 2 inches at planting time.

Thanks for the responses. I went back to my notes to check my info... they weren't planted 6" deep, it was more like 2-4" (as in, I placed the seed potatoes on the soil mix and then added ~4" of soil on top, so the tops of the seed potatoes were 2-3" under the top soil surface). I think I got them out there the last week of April... so, more than 'a few weeks ago' as I originally posted, but still several weeks later than I should have (last frost date here is May2).

So, it sounds like I might still be okay with these potatoes? How long does it typically take to see foliage? It's been over a month at this point.

You might. Depends on the soil temps and the variety. They need cool soil temps for best growth.

and then added ~4" of soil on top, so the tops of the seed potatoes were 2-3" under the top soil surface).

But if you added 4" of soil on top they were still buried too deep to begin with. Trench planting works great when the seed potatoes are just lightly covered but not covering them with that much soil until after the begin growing..

Dave

Well let this be a lesson to me. I planted 5 potatoes this year, and always thought they were supposed to be planted about 6" deep. Mine took a long time to come up and that's probably why. Had almost given up on them, but they all emerged and are now growing vigorously.

I plant mine about 5 inches deep with no problem, Planted 2 week of april and they are now flowering, Looking as good as they ever have but we had excellent weather for them.

There is a good rule about covering any size seed:
-- ABOUT TWICE THE THICKNESS OF THE SEEDS.

If you lay down a potato lengthwise , it is about 1 to 1 1/2". So cover it with twice that : 2 to 3". Half an inch plus/minus would be ok.

Based on the OP revision it doesn't seem like either season or depth of planting is the problem. Something else going on.

Dig up a seed tuber and see what the deal is.

I think slow emergence has to do with the dormancy level of the potatoes. Even when I green up potatoes on my kitchen table and wait until the sprouts start to swell, they sometimes take their time coming up.

I had given up hope on a bed planted late and replanted it with sweet potatoes two weeks ago. Now two regular potato plants have decided to grow there after all. I'll move them, because I've found that I can usually succession plant potatoes here in the mountains. In rainy years late blight takes the late crop, though.

Possibly related to the variety based on my experience this year. I ordered 2 varieties and planted them in the 2 halves of a bed. Everything was done exactly the same for both varieties yet, as of a week ago, one variety was hilled for the second time and is now flowering. The other variety is still only breaking ground with shoots. BTW, none of the seed pieces were chitted prior to planting, never making that mistake again.

I donned a pair of garden gloves today and started digging around in the potato bin/cage and here is what I found...

In all but 2 cases the seed potato (I had planted whole potatoes, did not cut them up for planting) was basically a sphere of rotted mush, but they were each surrounded by 6-8+ little baby potatoes some as small as a pea, most more like the size of a grape or cherry tomato. Two of the 7 or so total seed potatoes were still firm but I did not dig them all the way to inspect more closely.

I scooped out the rotted seed potatoes but left the little baby potatoes in the soil, hoping that they might grow... they did seem to have their own little roots, their skin was bright pink, and they looked very healthy. The two as-yet unrotted seed potatoes I left in as well and tried not to disturb them too much.

Thoughts? This was my first attempt at growing potatoes and I feel like in all the research I had done prior, I didn't come across anything like this.

I suppose I could dig up the little 'fingerling' potatoes and just make a meal of them, but I'd rather give them a chance to grow if there is a possibility that they could actually grow at this point. It really doesn't feel that far into the growing season here (even though others' zone 6 gardens are producing already)... my volunteer tomato plants are only about 3-4 inches tall right now and the plants I started (tomatoes, cukes, zukes, pumpkins, beans, peas) are only just starting to take off.

Can I bump this? I'm not sure if I should just dig up the baby-sized potatoes and make a meal of them or give them a chance to grow now as new 'seed potatoes'.

Thoughts on what happened? Opinions on which route I should take at this point?

Still no greens at all?

Emorems, my guess is that your seed potatoes were unhealthy to begin with. I've had issues when i've planted potatoes from the previous years' harvest. Compared to certified seed potato that i've purchased, my saved potatoes have produced very small plants and low yields. Sometimes the plants fail to emerge at all. Some of these plants that failed to emerge may have produced small tubers like yours, but i never dug them up specifically to check.

If i had a bit of room at the end of my potato row, i used to plant a few potatoes from the previous year, but i don't bother anymore. They never do well. Not sure if that's your issue or not, but next year you might want to purchase seed potatoes instead.

It's pretty late in the season, but Maine Potato Lady still has some varieties of potatoes available. It's not ideal to plant this late, but if you tried an early season variety you might get some sort of crop.

Depends when you planted them, They might still be growing an you just dug them too early,Too much water may have made them mushy, I always use my potaotoes that are left over from the year before with no problem, But I do cut my potatoes so there is only 1 or 2 eyes and also fertilize with 10-10-10, Potatoes usually or done growing after the plants have flowered and die off.