Are my Potatoes Mush?

I'm having trouble picturing this. I think you mean you built a box to hold the straw, right?

If the plants are/were growing, I suspect they should have good potatoes under them. Sometimes the original piece of potato will rot away after the plant gets started, especially if it was large, so maybe you found that. Have the plants died yet? That's when they're ready to harvest.

Extra moisture (or very hot, dry conditions) can certainly cause potato sets to rot, but in that case, they don't make plants. I'd remain cautiously optimistic until you actually try to harvest them and see what's there.

Doesn't sound good to me either.

If anything was *EVER* going to mold and/or rot, this spring in the northeastern USA certainly gave it the ideal conditions for so doing.

Pat - In Zone 5

I guess I'd just wait and see. Your plants look very healthy, and I'm not sure if it's possible to have big healthy plants if something's going wrong beneath the surface.

but taking Aaron's word for it that the plants are healthy, you may have nothing to worry about.

I plant my seed potatoes in the soil and mulch with chopped straw as they grow. (In fact, I think I ought to top off the mulch this weekend.) The mulch usually gets a bit rotten at the bottom, sometimes with weird ear-shaped fungus thingees on it. The potatoes underneath are fine though (unless they've been nibbled by voles, which is a whole 'nother problem).

Remove the trailing slash, and they should display okay.