Did you plant them at the same time? Potatoes are supposed to eventually look bad.

Betty- yes they were planted at the same time. But the ones on the right never set blooms?

The pots look to be the same size. Is the soil the same? What about varieties? And yes, potatoes are supposed to eventually look bad, but not until they've reached their full growth and bloomed like the ones on the left. It looks like a fertility issue to me, but without knowing more can't say more than that. Potatoes like slightly acid soil with good nutrients. It's getting late in the season, but you might try adding some compost or composted manure, watering well and hoping. I don't raise potatoes in pots, but if I did I would put no more than two good seed potato pieces per pot. Dawn is much more knowledgeable about diseases than I am. She may have some insight when she gets here.

Mulberry- everything is the same...same seed potatoes, same soil, same size pots..The only thing I could think of is the one in question might get a bit more water then the other? Who knows.
If I can't save them, its not a huge deal, it would just be nice.

Bre, Look closely at the brown/tan spots on the leaves. Do you see concentric circles within them? Or areas of small circles?

If the leaves were only yellow, I might think the plant just needs to be fed (and I think the lighter color of its leaves does indicate it needs to be fertilized). With the brown spots or splotches on the leaves, it seems more likely to be a disease.

As for blooming, with potato plants, blooms are caused by exposure to cool temperatures, but the plants have to be a certain size before they'll bloom. Some potato plants bloom, some don't, depending on their size and the state of their health when temperatures are cool enough to induce blooming. Most of my potatoes bloomed this year because we had recurring late cold nights, but some of them didn't bloom. The ones that didn't bloom will produce just as well as the ones that did, all other things being equal.

As far as a difference in performance, even when you cut a seed potato in half, you can get different performance from each half. One-half might have had more eyes/sprouts, for example, than the other.

Finally, potato plants stop setting and sizing tubers once soil temperatures reach 85 degrees. That is one reason why yields tend to be smaller in pots---being above ground and lacking the insulation provided by the ground, the soil in the pots heats up faster and that can result in low potato yields. If I had potatoes in pots right now, I'd put something around the pots to shield them from the direct rays of the sun.

I have one tall raised bed on the west side of my shed that is filled with lush, beautiful and very well-mulched potatoes. To keep the soil in that bed from getting roasting hot in the afternoons and evenings when the sun is shining on it, I have grass clipping mulch 18" tall and 10-12" wide heaped up all around the outside of the raised bed----so it looks like I am growing potato plants in a gigantic heap of grass clippings. Even in raised beds, the soil can heat up faster than with grade-level soil, so it helps to keep the sun from directly hitting the sides of the raised beds just as it helps with pots.

If you have concentric circles within the brown or tan spots and splotches on the yellow leaves, we need to talk about Early Blight.

Dawn

Here is a link that might be useful: Soil Temp In-Ground 4

Ok, Ms. Dawn- I went out and looked for circles within the brown spots..they are just plain old brown spots. It kind of reminded me of something that was watered in the morning, and left to sit with water on its leaves in the blistering heat. But I don't water in the mornings.

But, all those yellow leaves in that picture I just took yesterday afternoon...gone..the leaves shriveled up and the stems fell off. What I did notice that I guess I hadn't before bc I don't go out there this time of day, is the one in question was in sunlight, and the other was still nicely shaded. So I moved the bad one into the shade also. I will kick it some fertilizer this evening when I make my rounds to see if anyone needs watered. I will see if I can round up some hay bales to put around them, and try to mow tomorrow for clippings.