A Comparison of Florida Hardiness Zone Maps
The average lowest minimum temperature for Zone 9a is 20 to 24.9 degrees and 25 to 29.9 degrees for Zone 9b. In Zone 9b most frosts last a night or two and rarely does the temperature dip below 30 degrees for any appreciable amount of time. But if you garden in Zone 9b with the expectation that you will never suffer a severe killing frost, you are doomed to failure. In 1962 Tampa experienced a record low of 18 degrees, a temperature that will kill most tropical plants and can even cause major damage to temperate climate shrubs such as azaleas.
Like most things in gardening, you have to be flexible when it comes to dealing with the cold snaps. I have found that, other than taking basic steps to protect my tropical plants during a frost, I have to accept that every two or three years I am going to lose some plants to a frost and likely once every 10 or 15 years I will suffer a major loss.
You would think that part of the solution to this dilemma would be accurate hardiness zone maps that would provide concise information on predicted periods of frost. However, the two maps below illustrate how difficult it is to predict what plants will survive in your garden. While the USDA Map is the generally accepted source for hardiness zones in the US, the Florida Climate Center Map was produced using the same methodology, but more current historical temperatures. The result is a map with many of the zones shifted north.
For a more detailed explanation of Hardiness Zones, click here.
Florida Climate Center Hardiness Zone Map*
*Note, the Florida Climate Center Web site recently went through a major revision and the Hardiness Zone Map is no longer available.