Hi Dawn,
For your information, I made a cold frame out of hay bales last fall
to overwinter pots of perennial seedlings and small shrubs.
Unfortunately, mice found the cold frame and made it their home,
consuming most of the plants. Most annoying. Hopefully you will not
have the same experience this time of the year.
I would think a southern exposure is best. You could probably put the
seedlings out right now, especially if you cover the frame with an
extra blanket if frost is expected. Keep the seedlings shaded to
begin with and increase the sun exposure over two weeks or so. Good
ventilation on sunny days is important. Good luck!
Eva Thorn
Solon, Ohio z5 (last frost May 17)