Figure 5. A typical pattern of acclimation to freezing temperatures by woody plants. Temperatures and dates vary depending on hardiness zone and plant species.
Illustration of hardiness from September (least hardy) through November (full hardiness) and acclimation stages starting at the end of September and mid-October.

Source: Principles, Practices and Comparative Costs of Overwintering Container-Grown Landscape Plants. Southern Cooperative Series Bulletin 313, May 1986. David J. Beattie, editor. Pennsylvania State University.