This is a question many people are asking, Julia, after the last couple of winters we have had when so many people lost so many plants. But you actually have many choices, and I would encourage you to start by looking at Florida native plants. These are plants that are used to the extremes our weather can bring: full sun and intense heat in the summer and below-freezing temperatures in the winter. They also are used to our fluctuations in water. Some of my favorites are wax myrtle (Myrica
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cerifera), Simpson stopper (Myrcianthes fragrans), Walter's viburnum (Viburnum obovatum) and coontie (Zamia pumila). If you are looking for a tree, consider one of our native hollies or the Southern magnolia. All of these will thrive in your yard, even with a freeze.
the site below was informative
http://www.ehow.com/list_7665392_cold-hardy-...