Planting Zones Explained: Hardiness, Heat, and Microclimates

Just as a driver needs a map, a gardener needs planting zones to know which plants will thrive. The USDA Hardiness Zone Map divides the U.S. into zones based on average annual minimum winter temperatures, each zone spanning 10°F (revised in 1990 to 5°F subzones). Metro Atlanta falls in Zone 7a (0–5°F) to 7b (5–10°F). Plant labels list hardiness zones; a plant rated for Zone 7 should survive Atlanta winters.

But winter cold isn't the only factor. A plant hardy in Zone 7 in cool-summer California may melt in Georgia's heat. The American Horticultural Society's Heat Zone Map addresses this, mapping regions by average days above 86°F. Atlanta is in Heat Zone 7, matching its cold zone—a helpful coincidence.

Pushing the Envelope

Gardeners love creating microclimates to grow plants outside their rated zones: digging up bananas each winter, using fans to cool bentgrass putting greens, or hunting for cold-hardy oleanders. Zones are guides, not absolute rules. One of gardening's great pleasures is "growing outside the box."

More Information: USDA Cold Hardiness Zone Map