by Keith Baldwin, Farm Services Coordinator


Sweet potato roots are referred to as “green” immediately after harvest and are usually not as sweet as cured sweet potatoes. Commercially, most roots are cured immediately after harvest to improve flavor and storage life. Curing the sweet taters heals cuts and reduces decay and shrinkage in storage because it allows the “skin” to thicken and reform, in effect healing bumps and bruises. Curing also converts some starches to sugars, enhancing flavor.

Curing should be started immediately after harvest and continued for 4 to 7 days at 80 to 85 degrees and 90 to 95 % relative humidity with good air circulation and ventilation. 100% relative humidity should be avoided so that the surface of the sweet potatoes will not be completely wet, which promotes disease. The warmer the soil temperature when roots are harvested, the quicker they will cure.

Long-term storage areas should be maintained at 55 to 60 degrees with 85 % relative humidity and with sufficient venting to produce a total volume change of air at least once a day. Above 60 degrees, internal breakdown, shrinking and sprouting can occur. Temperatures below 55 degrees may cause hardcore, a disorder where a whitish, hard area appears in the cooked sweet potato.




When it comes to choosing cultivars, short-day onions are the way to go in the Carolinas. These are the onions that begin to bulb when day length in the spring reaches 12 hours. Probably the most famous short-day onion in these parts is the Vidalia onion, named for a region in Georgia and also known as Granex 33. Other sweet onions to try are Early Grano, Candy, Stockton Sweet Red and Texas Grano. Unfortunately, sweet onions are not particularly good keepers.

Growing onions in the Carolina is a somewhat tricky business. Planting dates are determined by where you live and what sort of “start” you use. Onions can be started as seed in the field, sets (small, immature bulbs that should be about one inch in diameter) and as transplants. Onion sets can be planted in fall or early spring. However, onions grown from sets do not make the best bulbs, are rather costly, and are not recommended for commercial plantings.


Onions from Seed

Direct seeding for bulb onion production is done in the early fall. In the Coastal Plain of the Carolinas, the seed can be planted directly into prepared beds from mid-September to mid-October and from mid-January to the end of February. Sow seed about 1/2 to 3/4 inch deep with about 8 to 12 seeds per ft. of row. Planting earlier creates a risky situation where plants can get to big (greater diameter than a pencil) and then bolt rather than bulb in the spring.

Direct seeding of onion is not recommended in the Piedmont in North or South Carolina nor in Western NC Mountains or Upstate South Carolina.


Onions from Transplants

Onions grown from transplants should be planted in the early spring for best results.  Transplants can be set in March in the Piedmont and somewhat earlier in the Coastal Plain (February). Set plants at a uniform depth, with the bottom of the plant about 1 to 1.5 inches below the surface of the soil. Set 2 to 4 plants per foot of row for large bulbs and 4 to 6 per foot for medium bulbs.

Most often plants are purchased from certified plant growers in the southern states. Anyone in the Coastal Plain (and risk-takers in the Piedmont) interested in growing their own transplants can seed outdoors in protected beds in early fall. These seeds are planted about 1/2 inch deep and in rows about 4 inches apart at the rate of 8 to 10 seeds per inch. About 3/8 oz of seed will produce enough transplants for 1000 square feet of planting. Seeds should be planted October 1 to 15. Beds should be protected when temperatures reach 20 degrees F or below.


Harvesting your Onions

Looking ahead, about a month before harvest, it is best to start working the soil away from the bulbs. This process should involve 2 or 3 cultivations so that about 7 to 10 days before harvest time, the bulb is about one-third above ground, which hastens bulb and neck drying. Harvest when 75% or more of the tops fall over. Curing is very important. If the “necks” are not thoroughly dry, neck-rot can occur. Temperatures of 90 to 100 0F will hasten the curing process.

The table below outlines planting dates for South Carolina (from Clemson University).





Onion Sets



Mar. 1-30

Sept. 1-Oct. 30


Feb. 15-Mar. 15

Sept. 15-Nov.15

Coastal Plain

Feb. 1-Mar. 1

Oct. 1-Nov. 30


Onion Plants



Mar. 1-30


Feb. 15-Mar. 15

Coastal Plain

Feb. 1-Mar. 1


Onion Seed




Sept. 15-Oct. 15

Coastal Plain

Oct. 1-Oct. 30


Sources for more information:

Planting and Harvesting Guide for Piedmont Vegetables and Herbs

Doug Jones, Piedmont Biofarm and Debbie Roos, North Carolina Cooperative Extension, Chatham County Center


Onion, Leek, Shallot & Garlic Clemson University Extension HGIC 1314

Karen Russ, HGIC Horticulture Specialist & Bob Polomski


Time to Plant Onions and Garlic

Charlotte Glen, NC Cooperative Extension