Southeast

ZONE 25. South Florida and the Keys
Growing season: all year. Add ample year-round rainfall (least in Dec. through Mar.), high humidity, and overall warmth, and you have a near-tropical climate. The Keys are frost-free; winter lows elsewhere run from 40 degrees to 25 degrees F/4 degrees to -4 degrees C.

ZONE 26. Central and Interior Florida
Growing season: early Feb. to late Dec., with typically humid, warm to hot weather. Rain is plentiful all year, heaviest in summer and early fall. Lows range from 15 degrees F/-9 degrees C in the north to 27 degrees F/-3 degrees C in the south; arctic air brings periodic hard freezes.

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 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.