Beginner Gardening: Potatoes, how deep to "earth up" (cover)?, 1 by CapeCodGardener

CapeCodGardener wrote:
Hi! Growing my first potatoes this year, in SmartPot containers. I read that you're supposed to keep the plants covered with soil as they grow, to encourage more potatoes to grow from the stem. My question is: how much of the emerging foliage do I cover up as the vines grow? I've read everything from "cover completely" to "cover leaving some of the foliage showing."
Is there any definitive amount of stem to cover?
These are my vines this morning; they had reached 5-6 inches in height, so I covered them up but left 2-3 inches of stem and leaves out in the air.