Billbergias, Nidularia, Bromelia, Dyckia, Puya some Neoregelias and some Aechmeas can take some 20's. Marie Selby Gardens in Sarasota has a list online that gives the hardiness (through scientific proof...ie they put the plants out and left them out in temperatures between 20-32F and saw what made it, when it got damage and when it got killed) you can find it online. Its old now. I cover stuff with frost cloth if its going to be below 26-32 for a period of hours and hours but those temps for a brief time that plants are ok in my yard anyway....your mileage may vary! My Dyckias have been yard residents for 15 years and have survives a lot of cold.
