Okra, year-round sweet potatoes and greens, and pecans are just some of the seasonal fruits and vegetables you'll find in the South and Southeastern states. In the more southern areas, the climate can be warm enough so growing seasons almost flip-flop with the rest of the country, and the height of summer months can mean there's little at the market besides okra—everything having given up in the heat—whereas green beans and tomatoes pile high during the winter month.
Exact crop availability and harvest times vary locality-to-locality and year-to-year depending on the exact weather conditions, but this summary will help you know when to look for what at markets near you in the South.
Apples, mid-August through February (varies greatly by specific region and often available from cold storage in the winter months)
Asparagus, mid-April through June. Skinny spears may be in fashion, but fat asparagus can be just as tender.
Beets, May and June, and again in the fall. Look for spring beets with their green still attached (cook them like turnip greens).
Blackberries, July and August.
Blueberries, end of May through August.
Broccoli, April and May. Like other cruciferous vegetables, broccoli takes on a bitter taste when exposed to much heat when it's growing, so it's planted in the fall or winter and harvested in the spring in warmer areas.
Butter Beans, mid-July through August for fresh; dried versions available all year
Cabbage, May through December
Cantaloupes, July and August
Cauliflower, April through June
Collard Greens, year-round
Corn, mid-June through mid-August
Cucumbers, June through October
Eggplant, mid-June through September, sometimes even earlier in the hottest of areas
Figs, August and September
Grapefruit, winter and spring
Grapes, August through October
Green Beans, June through September
Kale, best in fall and winter
Lettuce, fall through spring
Mangoes, May and June, most of the U.S.-grown commercial crop is grown in Florida
Okra, May through October
Oranges (Navel), winter and spring
Oranges (Valencia), spring and summer
Peaches, June through September
Peas, July and August
Pecans, November and December
Peppers, mid-June through October
Persimmons, October through December
Plums & Pluots, mid-May through July
Pole Beans, May through September
Potatoes, mid-June through July
Pumpkins, September and October
Raspberries, July through September
Strawberries, mid-April through mid-June
Squash (summer), mid-May through September
Squash (winter), mid-September through mid-December
Sweet Onions, spring and summer
Sweet Potatoes, harvested July through October, available year-round
Tomatoes, July through October, although they're often available for even longer in the warmest areas
Watermelons, June through August
Winter Squash, mid-September through mid-December
Zucchini, June through October
Zucchini Blossoms, spring and summer, look for fresh, just-picked specimens for the best texture and brightest flavor
Many root vegetables and frost-friendly cruciferous vegetables like cabbage, kale, and broccoli, will fair quite well through the South's often mild winters, so those items may show up for months after what's listed here, especially if winter is a mild one that year.
Remember, you may well see items at farmers markets well before (or after) they are listed here. Ask the farmer about where and how they're grown. Maybe that farm has unique microclimate conditions that allow for early or late harvest, maybe they've been driven in from the different part of the state or region.