Give it time to grow. It may take a few years.

Deleted duplicate post.

This post was edited by susanzone5 on Mon, Jul 1, 13 at 21:37

It will also self-seed, at least mine has, and it grows very well.
Also, it is pretty late to come out of the ground in spring. Mine is currently covered with honey bees.

In my experience the tuberous rooted, perennial species of milkweeds are slow growing for the first few years. Your plant probably won't be a large bushy plant for about 2-3 seasons. Although it's hard, you'll need to have patience for this one.