According to the USDA Key West is in USDA Zone 11b. Here is some general info for USDA Zone 11b to help you get started.
Average Date of Last Frost (spring) | Never |
Average Date of First Frost (fall) | Never |
Lowest Expected Low | 45°F |
Highest Expected Low | 50°F |
This means that on a really cold year, the coldest it will get is 45°F. On most years you should be prepared to experience lows near 50°F.
You can view the USDA Zone map for Florida here:
Below is a list of planting guides for Key West, FL. These guides are based on data from Zone 11b.
Vegetables
Herbs
Flowers