Guidance for overwintering container grown ornamentals
Maintaining stable conditions while overwintering container grown plants can be a challenge. To help, the University of Massachusetts-Amherst has developed guidance for overwintering these plants.
A nice summary of the guidance with commentary is available from Nursery Management
In addition to discussing various systems for covering plants, guidance is provided for specific temperatures and individual species. The full guidance is available from UMAss Amherst at this site