I started C. lanceolata and clematidae from seed last year and they spent the winter in a nursery bed. It's too early here (I'm in zone 4 too) yet to know how they will overwinter, though the person I got the lanceolata seeds from is in zone 5 and has grown it successfully there. I'll try to let you know how they come through.

kms

If you're looking for an inexpensive way to try codonopsis, Codonopsis clematidea is very easy to grow from seed. I got seed from the Rock Garden Society seed exchange, and, two years later, I had plants in bloom.

Good luck,
Janet