I wish my purple milkweed plants grew as vigorously as yours. It's fine to plant the Echinacea purpurea now. When I've transplanted them in spring, they struggled through early heat waves that severely weakened them. I would do it soon, so they can adjust and put on some root growth before winter. What kind of soil is in your nursery bed?

It's a raised bed with bagged topsoil, compost and some sand in the top in the top 5 or 6 inches then my rocky compacted soil underneath. If they were small, they would've been very easy to dig out. lol

A few of my purple milkweed plants grew a foot tall over the summer but some are still only three inches tall. Big roots for such tiny things. I also planted several in a permanent place this spring instead of the nursery bed. About half of those are still alive. I'll be so disappointed in they don't come back next spring. My original plant that I took the seeds from has taken years to grow into a decent size. The flowers are a beautiful color when it blooms and it's my favorite for Monarchs. They do well on it and so far it seems like it's not as badly attacked by aphids as swamp milkweed and tropical milkweed.