I hope the stem is still green - new growth can come out from the nodes if they are.

Are you familiar with cloches? These are basically large bottles placed over plants overnight to protect from marginal cold. Cardboard boxes also work.

It helps to know your microclimate (shade vs. sun; low pocket, hillside, top of knoll, flat plain; compass relation to house, which has relevance to cold vs warm wind blockage and time of sun exposure; etc). Also, what is your USDA floral zone and location (state, at least)