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

Three regions, one long season

NOAA’s state climate summary describes North Carolina as humid, with very warm summers and moderately cold winters. Three landforms divide it: the Appalachian Mountains in the west, the Piedmont plateau in the middle and the Coastal Plain in the east. Elevation runs from sea level to more than 6,000 feet, the largest range of any state east of the Mississippi. Average annual temperatures differ by more than 20°F between the highest peaks and the coast. The mountains also partly block cold air from the Midwest, which softens winters.

NC State Extension builds its planting guidance on the Piedmont and adjusts from there. The Extension Gardener Handbook says fall planting dates can run 10 to 20 days earlier in western North Carolina and 7 to 14 days later on the Coastal Plain. The soils differ as well. In the Piedmont and mountains, soil forms from weathered bedrock called saprolite. The handbook contrasts the well-drained Cecil soils typical of the Piedmont with poorly drained Coastal Plain soils such as the Coxville series.

Planting by season, not just by frost

NC State Extension’s Central North Carolina Planting Calendar for Annual Vegetables, Fruits, and Herbs is built around three seasons. Spring and fall have short days and cool temperatures, and summer has long days and heat. Cool-season crops tolerate some frost. Warm-season crops belong outdoors only in frost-free months, and even they pause during heat waves in the mid 90s °F. Freezes, high heat, humidity and strong sun can all stress plants in central North Carolina. The calendar’s answer is to choose varieties that tolerate temperature extremes, plant at times that avoid them, or protect the plants.

Key points from the calendar:

• Plantings set in the middle of each recommended window do best. Success drops toward either end.
• If you grow your own transplants, start them six to eight weeks before the transplant date and harden them off gradually.
• Spun-woven row covers let you start earlier in spring and keep going later into fall. Plastic mulch brings crops in earlier.
• Use planting dates to avoid pests. Delay fall planting until whiteflies decline with cooler weather, and delay spring planting until the soil warms to cut fungal and bacterial disease.
• Replant every few weeks within a window to stretch the harvest.

Use the frost dates for your city above to find where each window falls for you.

The fall garden

North Carolina’s fall garden is a real second season. The handbook names August as the main fall planting month. In the Piedmont, crops that take 60 to 80 days go in around August 1, and turnips and other fast greens can wait until about September 1. Suitable fall crops include beets, beans, broccoli, Brussels sprouts, cabbage, cauliflower, carrots, collards, kale, kohlrabi, leaf lettuce, mustard, radishes, rutabagas, spinach, turnips, southern peas and sugar snap peas. Cold-hardy collards, kale, turnip greens, spinach and Swiss chard planted in fall may survive the winter and grow again in early spring.

The handbook also cautions that insects and diseases can be worse in fall, because populations build through spring and summer. Direct-seeding broccoli and collards in late summer works only if you can keep the seedlings moist. Without irrigation, buy transplants instead.

Heat, humidity and pests

Summer heat makes cool-season crops bolt and turn bitter. The handbook suggests shade cloth or taller crops to stretch them into summer. Late summer is when cool-season crops go back in for fall. The calendar recommends disease-resistant varieties and explains the label codes: V for Verticillium wilt, F for Fusarium wilt, N for nematodes and T for tobacco mosaic virus. Codes vary by seed company, so check each company’s key. For specific variety picks, NC State points gardeners to its local Extension agents and Extension Master Gardener volunteers.

NOAA notes that summers from 2005 to 2020 were the warmest on record for the state, with the most very warm nights coming in 2010 to 2020.

Fix the pH first

The handbook is blunt about soil. North Carolina soils are acidic, like nearly all soils in the Southeast, and unlimed native soil often tests pH 4.5 to 5.5. Most vegetables do best at 6.0 to 6.5. Lime reacts slowly, so a fall application can correct acidity before spring planting. Sandy and heavy clay soils both improve fastest with repeated additions of organic matter. Work 2 to 3 inches of rotted leaves or compost in each spring and again after the fall harvest, or plant winter rye, ryegrass or wheat as a green manure.

NC State Extension sends gardeners to the NC Department of Agriculture & Consumer Services for soil tests. Forms and sample boxes are available at any county Cooperative Extension center. Test before planting and every two to three years after. The handbook calls inexpensive home kits unreliable.