Mound 'em up when they just start to look leggy.
My friend used to pile old tires up around his tater plants and fill 'em with mulch and soil as they grew.
Always had lots of potatos.

Are we talking about sweet potatoes? Or can you grow white potatoes up there?

Actually, Katkin, they're red potatoes, but white would also grow just as well. What sort of temps and soil do sweet potatoes like?
Thank you treefrog.

I don't think I can grow white or red potatoes this far south. But sweet potatoes grow ok. Sweets like the heat and lots of water.

A friend grew regular white potatoes one year here in south Fl. I told him I didn't think they'd grow here. But you can't tell an old Minnesota boy he can't grow potatoes.
Well he started them in a well composted spot, mulched heavily. He put a used tire around the "hill". Every time the leaves would get taller than the tire he would add another tire. He kept it growing upward, filling with compost, mulch, leaves and soil, leaving only the top leaves showing. By the time it was 4 or 5 tires high the leaves browned off, so we pulled them off, harvesting a surprising number of nice potatoes. Much to my surprise.

I've seen people up north grow potatoes using old hay around and over the plants till it became a nice pile by the end of the season. Easy harvesting.