I vote to move your foxglove seedlings outside for the winter. Foxgloves are biennials so they need two years of growth before they bloom and they have enough sense to go dormant in the winter and are not bothered by winter weather - with some exceptions. They do need good drainage and should not be fertilized in the fall - wait until you see signs of new growth in the spring. With so many young upstarts it would be a good idea to keep a few in the greenhouse and a few in pots outdoors. Then if some freak weather destroyed the new seedlings you would have a back up supply. Congrats on your green thumb and Keep Growing, Marianne Binetti