Answer: Monrovia rates this plant for USDA zones 10-11. USDA zone 11 has average annual minimum temperatures above 40 degrees F. USDA zone 10 has average annual minimum temperatures of 30 to 40 degrees F. So, yes, like your bougainvillea in the earlier question, the hibiscus should also be covered if temperatures are predicted to drop below 30. To download a free publication called Frost Protection from the University of Arizona Cooperative Extension, go to their publications website: http://ag.arizona.edu/pubs/ and search for Frost, and click on Gardening and Publication in the pulldown menus. Publication AZ1002 can be retrieved as a pdf file. It contains detailed instructions on covering plants.
Q&A Library Searching Tips