From the Atlantic:
To an experienced potato person, the fact that all small potatoes are NOT new is a given. But to most 21st century Americans, "new," as Rodger pointed out, has come to be considered a size instead of what it ought to be, which is a real-time adjective that refers to the newly dug potatoes that come out of the ground only at the start of the summer season. The problem is that, although size might matter slightly in terms of eating experience, the main draw to new potatoes is how good they taste, which is very different from matured potatoes that have been stored for many months.
What makes the difference between these new potatoes and those small-in-size-but-not-new potatoes we get the rest of the year?
I asked Molly Stevens to explain for me since she wrote a whole book on potatoes and she knows a lot more than I do. "The most important point to make," she wrote back, "is that new potatoes should be treated the way you would any fresh-from-the-market perishable produce. Because of their high water content, they spoil and wilt the same way a fresh tomato or summer squash would. I make the connection between green, spring onions and papery storage onions." Makes sense and it's true. Really working with new potatoes is an entirely different potato experience than we get the other 10 or 11 months of the year.
New potatoes are awesome. I can also testify to the short storage time... the new potatoes I bought a little while ago (pictured above) started getting soft almost right away. Boil and eat them as soon as you can.