Charmion, I hope Steve/TGT explained (or you knew) that most established potted perennials can go into the ground as late as weeks before the first frost. They may not fully flower that year, but the real magic of the plant happens underground, and the roots will reward you the following year.

I planted Coral Bells that way several years ago, and have based my whole gardening plan on fall planting. Just keep the roots as watered as each plant calls for no matter how unlike their future selves they look, and attack weeds with your usual pluck. You'll see those mature beauties soon enough (starting next spring and summer). Potted annuals-- set right on top of bare spots between the perennials-- can give good cheer this season.