Gardening in South Carolina: zones, frost dates and when to plant

Piedmont and Coastal Plain

Clemson Cooperative Extension’s Planning a Garden fact sheet (HGIC 1256) splits South Carolina into two planting regions. The Piedmont covers the Upstate and the northern tier, including Greenville, Spartanburg, Anderson, Oconee, Pickens, York, Lancaster and Chesterfield counties. The Coastal Plain covers the Midlands and the Lowcountry: Richland and Lexington, Aiken and Orangeburg, Florence and Horry, and the coastal counties from Beaufort and Jasper to Charleston and Georgetown.

The planting chart gives each region its own spring and fall windows. Spring starts several weeks earlier on the Coastal Plain. Cabbage, for example, can go in from early February there, but not until mid-March in the Piedmont. In fall the order flips: the Piedmont’s fall windows close earlier, while the coast can keep seeding cool-season crops later in the year. Match the chart’s region to your county, then check the frost dates for your city above.

Rainfall varies more than the two-region split suggests. NOAA’s state climate summary reports about 80 inches a year near Lake Jocassee in the mountains of the far northwest. Wateree, in the Midlands, gets less than 39 inches, the driest spot in the state. Most of the Upstate and the Lowcountry average 45 to 55 inches. On the Coastal Plain, summer sea-breeze thunderstorms add a little extra.

What limits South Carolina gardens

Heat drives most of the calendar. Clemson notes that cool-season crops grow poorly in summer heat, so they belong in late winter, spring and fall. Warm-season crops need warm soil to germinate and are killed by freezing temperatures. That is why HGIC 1256 recommends a spring, a summer and a fall garden plan, not just one.

Weather adds more risk. Severe thunderstorms that can produce tornadoes come in late winter and spring, and hurricanes arrive in summer and fall. NOAA also notes that rising temperatures dry soil faster during dry spells, which makes droughts more intense. Clemson advises siting the garden close to a good water supply because vegetables need water during droughty periods.

Below ground, root-knot nematodes are a widespread problem. Clemson says they are most common in the sandy soils of the Coastal Plain and river deltas. These microscopic roundworms feed on roots and leave knots or galls that can keep plants from taking up enough water and nutrients. Infested plants may look stunted and wilt easily in hot, dry weather. Because other problems look similar, Clemson says to confirm nematodes by checking the roots or with a lab test.

Clemson Extension’s planning advice

HGIC 1256 suggests drawing the garden on paper and ordering seed by January or February. Some transplants can be started indoors as early as January. Other points from the fact sheet:

• Give the garden at least six hours of direct sun. Leafy crops tolerate partial shade, but tomatoes and peppers need full sun.
• Put tall and trellised crops on the north side, group crops by how long they take, and rotate plant families.
• On poorly drained or steep sites, build raised beds about 3 to 4 feet wide so you can reach the center without stepping in.

The chart also shows what fits each season. Okra, peanuts, sweet potatoes, Irish potatoes and sweet corn are spring-only crops in both regions. Brussels sprouts, garlic and onion plants are recommended only for fall. Collards, kale, mustard and turnips have both spring and fall windows. Lettuce has a fall window on the coast but not in the Piedmont. Pumpkins are planted in June or July.

Varieties that resist nematodes

Clemson’s HGIC fact sheet Root-Knot Nematodes in the Vegetable Garden lists resistant cultivars. They include ‘Charleston Belle’ and ‘Carolina Wonder’ bell peppers, ‘Carolina Cayenne’ and ‘Charleston Hot’ hot peppers, ‘Nemagreen’ lima beans, and southernpeas such as ‘Mississippi Silver’, ‘Colossus’ and ‘Clemson Purple’. Several sweetpotatoes are on the list too, including ‘Bonita’ and ‘Covington’. The same fact sheet recommends:

• rotating in non-host crops like corn, onions, garlic, asparagus and strawberries for about three years
• tilling every 10 days through a hot, dry summer fallow
• solarizing moist soil under clear plastic for 6 to 12 weeks
• planting French marigolds such as ‘Tangerine’ or ‘Single Gold’ solidly, no more than 7 inches apart, for at least two months before turning them under

Soil testing through Clemson

Clemson HGIC says vegetables do best at a slightly acidic pH of 6.0 to 6.5. The Clemson Agricultural Service Laboratory’s standard test reports pH, lime requirement and the major nutrients. Mailer kits are sold at county Extension offices, and you can also drop off samples there or mail them to the lab. Take cores 6 to 8 inches deep from at least 12 spots, air-dry the soil overnight, and fill the bag. The lab suggests testing a few months before planting, because pelletized dolomitic lime can take several months to change soil pH. HGIC staff and county agents can help you read the report.