I live in zone 7a which I think covers New York City. They are Peppermint hydrangea if that makes any difference. I have them currently planted in a 26" planter under my open foyer by the front entrance. Will they survive the winter and bloom in the spring? What can I do to ensure they don't freeze in winter short of bringing them in the house? Thanks!

They should be fine. The rule is that a potted plant needs to be able to withstand temperatures two zones lower. What I read on line says that Peppermint Hydrangea is hardy to zone 5. With the added protection of the house, it should work.

The bigger issue may be if they will get enough sun to bloom properly.

BTW, I Googled images of Peppermint Hydrangea. Gorgeous!