Ron,
You haven't stated what variety your nana plant is. You're in the same zone as I am, and if you have a basjoo, follow
Anyone in the northeast and you can see what I did. There were four pups from 2007, and each of them got their own pup in 2008, under the cover. When I uncovered in April 2009, I saw that they all made it. I dug, and potted, all but the largest of the 2007 pups (4½ feet) which I left. Shortly thereafter it produced several pups and, yesterday, I noticed another new one. There are now five pups from this year, and the plant is on it's seventh leaf.