Florida Hardiness Zone Maps

As described elsewhere on this site, national Hardiness Zone Maps have experienced several significant revisions over the past half century. This is clearly demonstrated by comparing the various attempts over this period to delineate between Zones 9 and 10 in Florida.

Let's start with the 1960 USDA Hardiness Zone Map. The image on the right is from the 1965 update to the map. Florida USDA Hardiness Zone Map 1965
This map of Florida is taken from the 1990 USDA Plant Hardiness Zone Map. Notice how Zone 9 (the brown and beige areas) has moved further south. In the map above Tampa and St. Petersburg are in Zone 10, while Orlando is in Zone 9. In the 1990 Map, Tampa and St. Petersburg are in Zone 9b along with Orlando. This movement south prompted some to speculate we were in a new ice age! Florida USDA Hardiness Zone Map 1990

In the 1995 Florida Climate Center update to the 1990 USDA Map St. Petersburg is in Zone 10a, Tampa is just over the line in Zone 9b and Orlando is squarely in the middle of Zone 9b.

Note, the Florida Climate Center Web site recently went through a major revision and the Hardiness Zone Map is no longer available.

Surprisingly, the 2003 AHS Draft Hardiness Zone Map looks closer to the 1960 USDA Hardiness Zone Map. Zone 9 has retreated northward. Tampa and St. Petersburg are back in Zone 10, while downtown Orlando is in Zone 9.

Zone 9 does show two small heat zones that defy an easy explanation - one is southeast of Orlando and one is south of Lakeland. Neither site is in a heavily populated urban area that would give off residual heat.

2004 Arbor Day Map shows that Zone 10 continues to creep northward.

The Arbor Day Map was updated in 2006. Even in two short years you can see differences. For example, Zone 10 is shown moving inland from the Tampa Bay area toward Orlando.

From 1990 to 2006 the Tampa Bay area has moved from being squarely in the middle of Zone 9 (USDA 1990 Map) to now being well within Zone 10.

The 2012 USDA map shows virtually no change from the 1990 USDA version with respect to how far south Zone 9 extends. However, the 2012 version does show Zone 9 extending further north into Georgia.
What is also interesting about the 2012 USDA update is that Zone 10a has extended north into the Tampa Bay region. It is possible that this is due to a urban heat island effect from these two cities.