http://www.senecahillperennials.com/ind ... =asclepias
Zone 4 ~ Height: to 60cm/2ft ~ Sun to part shade, average soil
Asclepiadophiles everywhere recognize this as the crème de la crème of the American milkweeds (pun intended). The full shining white flowers, each with a wine-colored ring at the base of the hood, crowd into luscious terminal umbels. In the wild it occurs in well-drained or somewhat dry woods and along roadsides, and we have had trouble getting it to persist in our relatively moist, fertile conditions. A correspondent in Arkansas writes "I have these milkweeds growing in partial shade, on a hillside, in the most stony, rocky, soil I have on my property. It's up toward the top of a hill. I do not baby any of them at all. They are on the worst soil I have and I completely ignore them. I don't even know how many I have. They have reseeded themselves." We suggest, therefore, that you grow them lean.
Apparently from my searches, it looks like it also has a taproot. Dig carefully and take as much as the taproot as possible. I usually put them into a pot and keep them in the shade and then transplant when they are out of shock.