Mints are perennials. While they might survive the winter in your greenhouse, it is also possible that they will be 鈥渃ooked鈥 (die)鈥攁ssuming like most glass structures your greenhouse heats up in the sunlight. You would be better off putting the plants, pots and all, into holes in the ground, surrounded by soil. (If the plants are pot bound now, consider transferring them into larger pots them before setting them into the ground. That way, if they do set roots, they will do it within the pot first.) That way, they will experience a 鈥渘atural鈥 winter: rain, snow, snow melt, etc. If you lift the pots in late winter/early spring before roots start spreading out, you should be able to avoid introducing the plant into the yard or garden. Then continue to care for them as potted plants, including putting them back into the smaller pots if you like (clip the roots, if nec to get the plants to fit).
Mints are perennials. While they might survive the winter in your greenhouse, it is also possible that they will be 鈥渃ooked鈥 (die)鈥攁ssuming like most glass structures your greenhouse heats up in the sunlight. You would be better off putting the plants, pots and all, into holes in the ground, surrounded by soil. (If the plants are pot bound now, consider transferring them into larger pots them before setting them into the ground. That way, if they do set roots, they will do it within the pot first.) That way, they will experience a 鈥渘atural鈥 winter: rain, snow, snow melt, etc. If you lift the pots in late winter/early spring before roots start spreading out, you should be able to avoid introducing the plant into the yard or garden. Then continue to care for them as potted plants, including putting them back into the smaller pots if you like (clip the roots, if nec to get the plants to fit).