ZONE 28. Gulf Coast, North Florida, Atlantic Coast to Charleston
Growing season: mid-Mar. to early Dec. Humidity and rainfall are year-round phenomena; summers are hot, winters virtually frostless but subject to periodic invasions by frigid arctic air. Azaleas, camellias, many subtropicals flourish.
ZONE 31. Interior Plains of Gulf Coast and Coastal Southeast
Growing season: mid-Mar. to early Nov. In this extensive east-west zone, hot and sticky summers contrast with chilly winters (record low temperatures are 7 degrees to 0 degrees F/-14 degrees to -18 degrees C). There's rain all year (an annual average of 50"), with the least falling in Oct.
ZONE 32. Interior Plains of Mid-Atlantic States; Chesapeake Bay, Southeastern Pennsylvania, Southern New Jersey
Growing season: late Mar. to early Nov. Rain falls year-round (40" to 50" annually); winter lows (moving through the zone from south to north) are 30 degrees to 20 degrees F/-1 degree to -7 degrees C. Humidity is less oppressive here than in Zone 31.
ZONE 33. North-Central Texas and Oklahoma Eastward to the Appalachian Foothills
Growing season: mid-April through Oct. Warm Gulf Coast air and colder continental/arctic fronts both play a role; their unpredictable interplay results in a wide range in annual rainfall (22" to 52") and winter lows (20 degrees to 0 degrees F/-7 degrees to -18 degrees C). Summers are muggy and warm to hot.
ZONE 35. Ouachita Mountains, Northern Oklahoma and Arkansas, Southern Kansas to North-Central Kentucky and Southern Ohio
Growing season: late April to late Oct. Rain comes in all seasons. Summers can be truly hot and humid. Without arctic fronts, winter lows are around 18 degrees F/-8 degrees C; with them, the coldest weather may bring lows of -20 degrees F/-29 degrees C.
ZONE 36. Appalachian Mountains
Growing season: May to late Oct. Thanks to greater elevation, summers are cooler and less humid, winters colder (0 degrees to -20 degrees F/-18 degrees to -29 degrees C) than in adjacent, lower zones. Rain comes all year (heaviest in spring). Late frosts are common.