Rhemannia elata (Chinese foxglove)

Aha found someone who grows this , I'm after a bit of advice Plantaholic, I've grown this plant from seed this year the plants grew huge so i planted them all out in the hope they'd flower this year but unfortunately they didn't , they are pretty huge and I'm in a bit of a dilemma what to do as I don't think they're hardy are they?, do you think I'll have to dig them all up or will a mulch do the trick .